Testing Background Functions

There are two distinct types of Cloud Functions: HTTP functions and background functions. Each type has its own testing requirements.

A function's test structure depends on which Google Cloud resources that function uses. In turn, a function's resource use depends on how that function is triggered.

This document describes how to test background Cloud Functions. See Testing HTTP Functions for information on how to test HTTP functions.

Pub/Sub-triggered functions

Pub/Sub-triggered function tests are structured differently depending on where the tested function is running.

Here is an example of a Pub/Sub-triggered function that prints "Hello, World":

Node.js

functions/helloworld/index.js 
/**
 * Background Cloud Function to be triggered by Pub/Sub.
 * This function is exported by index.js, and executed when
 * the trigger topic receives a message.
 *
 * @param {object} message The Pub/Sub message.
 * @param {object} context The event metadata.
 */
exports.helloPubSub = (message, context) => {
  const name = message.data
    ? Buffer.from(message.data, 'base64').toString()
    : 'World';

  console.log(`Hello, ${name}!`);
};

Python

functions/helloworld/main.py 
def hello_pubsub(event, context):
    """Background Cloud Function to be triggered by Pub/Sub.
    Args:
         event (dict):  The dictionary with data specific to this type of
         event. The `data` field contains the PubsubMessage message. The
         `attributes` field will contain custom attributes if there are any.
         context (google.cloud.functions.Context): The Cloud Functions event
         metadata. The `event_id` field contains the Pub/Sub message ID. The
         `timestamp` field contains the publish time.
    """
    import base64

    print("""This Function was triggered by messageId {} published at {}
    """.format(context.event_id, context.timestamp))

    if 'data' in event:
        name = base64.b64decode(event['data']).decode('utf-8')
    else:
        name = 'World'
    print('Hello {}!'.format(name))

Go

functions/helloworld/hello_pubsub.go 

// Package helloworld provides a set of Cloud Functions samples.
package helloworld

import (
	"context"
	"log"
)

// PubSubMessage is the payload of a Pub/Sub event.
type PubSubMessage struct {
	Data []byte `json:"data"`
}

// HelloPubSub consumes a Pub/Sub message.
func HelloPubSub(ctx context.Context, m PubSubMessage) error {
	name := string(m.Data) // Automatically decoded from base64.
	if name == "" {
		name = "World"
	}
	log.Printf("Hello, %s!", name)
	return nil
}

Java

functions/helloworld/hello-pubsub/src/main/java/functions/HelloPubSub.java 

import com.google.cloud.functions.BackgroundFunction;
import com.google.cloud.functions.Context;
import functions.eventpojos.PubSubMessage;
import java.nio.charset.StandardCharsets;
import java.util.Base64;
import java.util.logging.Level;
import java.util.logging.Logger;

public class HelloPubSub implements BackgroundFunction<PubSubMessage> {
  private static final Logger logger = Logger.getLogger(HelloPubSub.class.getName());

  @Override
  public void accept(PubSubMessage message, Context context) {
    String name = "world";
    if (message != null && message.getData() != null) {
      name = new String(
          Base64.getDecoder().decode(message.getData().getBytes(StandardCharsets.UTF_8)),
          StandardCharsets.UTF_8);
    }
    logger.info(String.format("Hello %s!", name));
    return;
  }
}

Unit tests

Here are unit tests for the Pub/Sub-triggered function above:

Node.js

functions/helloworld/test/sample.unit.pubsub.test.js 
const assert = require('assert');
const uuid = require('uuid');
const sinon = require('sinon');

const {helloPubSub} = require('..');

const stubConsole = function () {
  sinon.stub(console, `error`);
  sinon.stub(console, `log`);
};

const restoreConsole = function () {
  console.log.restore();
  console.error.restore();
};

beforeEach(stubConsole);
afterEach(restoreConsole);

it('helloPubSub: should print a name', () => {
  // Create mock Pub/Sub event
  const name = uuid.v4();
  const event = {
    data: Buffer.from(name).toString('base64'),
  };

  // Call tested function and verify its behavior
  helloPubSub(event);
  assert.ok(console.log.calledWith(`Hello, ${name}!`));
});

Python

functions/helloworld/sample_pubsub_test.py 
import base64

import mock

import main


mock_context = mock.Mock()
mock_context.event_id = '617187464135194'
mock_context.timestamp = '2019-07-15T22:09:03.761Z'


def test_print_hello_world(capsys):
    data = {}

    # Call tested function
    main.hello_pubsub(data, mock_context)
    out, err = capsys.readouterr()
    assert 'Hello World!' in out


def test_print_name(capsys):
    name = 'test'
    data = {'data': base64.b64encode(name.encode())}

    # Call tested function
    main.hello_pubsub(data, mock_context)
    out, err = capsys.readouterr()
    assert 'Hello {}!\n'.format(name) in out

Go

functions/helloworld/hello_pubsub_test.go 

package helloworld

import (
	"context"
	"io/ioutil"
	"log"
	"os"
	"testing"
)

func TestHelloPubSub(t *testing.T) {
	tests := []struct {
		data string
		want string
	}{
		{want: "Hello, World!\n"},
		{data: "Go", want: "Hello, Go!\n"},
	}
	for _, test := range tests {
		r, w, _ := os.Pipe()
		log.SetOutput(w)
		originalFlags := log.Flags()
		log.SetFlags(log.Flags() &^ (log.Ldate | log.Ltime))

		m := PubSubMessage{
			Data: []byte(test.data),
		}
		HelloPubSub(context.Background(), m)

		w.Close()
		log.SetOutput(os.Stderr)
		log.SetFlags(originalFlags)

		out, err := ioutil.ReadAll(r)
		if err != nil {
			t.Fatalf("ReadAll: %v", err)
		}
		if got := string(out); got != test.want {
			t.Errorf("HelloPubSub(%q) = %q, want %q", test.data, got, test.want)
		}
	}
}

Java

functions/helloworld/hello-pubsub/src/test/java/functions/HelloPubSubTest.java 

import static com.google.common.truth.Truth.assertThat;

import com.google.common.testing.TestLogHandler;
import functions.eventpojos.PubSubMessage;
import java.nio.charset.StandardCharsets;
import java.util.Base64;
import java.util.logging.Logger;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.JUnit4;

/**
 * Unit tests for main.java.com.example.functions.helloworld.HelloPubSub.
 */
@RunWith(JUnit4.class)
public class HelloPubSubTest {

  private HelloPubSub sampleUnderTest;
  private static final Logger logger = Logger.getLogger(HelloPubSub.class.getName());

  private static final TestLogHandler LOG_HANDLER = new TestLogHandler();

  @Before
  public void setUp() {
    sampleUnderTest = new HelloPubSub();
    logger.addHandler(LOG_HANDLER);
    LOG_HANDLER.clear();
  }

  @Test
  public void helloPubSub_shouldPrintName() {
    PubSubMessage pubSubMessage = new PubSubMessage();
    pubSubMessage.setData(Base64.getEncoder().encodeToString(
        "John".getBytes(StandardCharsets.UTF_8)));
    sampleUnderTest.accept(pubSubMessage, null);

    String logMessage = LOG_HANDLER.getStoredLogRecords().get(0).getMessage();
    assertThat("Hello John!").isEqualTo(logMessage);
  }

  @Test
  public void helloPubSub_shouldPrintHelloWorld() {
    PubSubMessage pubSubMessage = new PubSubMessage();
    sampleUnderTest.accept(pubSubMessage, null);

    String logMessage = LOG_HANDLER.getStoredLogRecords().get(0).getMessage();
    assertThat("Hello world!").isEqualTo(logMessage);
  }
}

Run the unit tests with the following command:

Node.js 

mocha test/sample.unit.pubsub.test.js --exit

Python 

pytest sample_pubsub_test.py

Go 

go test -v ./hello_pubsub_test.go

Java 

mvn clean verify

Integration tests

Here are integration tests for the Pub/Sub-triggered function above:

Node.js

functions/helloworld/test/sample.integration.pubsub.test.js 
const assert = require('assert');
const execPromise = require('child-process-promise').exec;
const path = require('path');
const requestRetry = require('requestretry');
const uuid = require('uuid');

const cwd = path.join(__dirname, '..');

  it('helloPubSub: should print a name', async () => {
    const name = uuid.v4();
    const PORT = 8088; // Each running framework instance needs a unique port

    const encodedName = Buffer.from(name).toString('base64');
    const pubsubMessage = {data: {data: encodedName}};

    // exec's 'timeout' param won't kill children of "shim" /bin/sh process
    // Workaround: include "& sleep <TIMEOUT>; kill $!" in executed command
    const proc = execPromise(
      `functions-framework --target=helloPubSub --signature-type=event --port=${PORT} & sleep 1; kill $!`,
      {shell: true, cwd}
    );

    // Send HTTP request simulating Pub/Sub message
    // (GCF translates Pub/Sub messages to HTTP requests internally)
    const response = await requestRetry({
      url: `http://localhost:${PORT}/`,
      method: 'POST',
      body: pubsubMessage,
      retryDelay: 200,
      json: true,
    });

    assert.strictEqual(response.statusCode, 204);

    // Wait for the functions framework to stop
    const {stdout} = await proc;

    assert(stdout.includes(`Hello, ${name}!`));
  });
});

Python

functions/helloworld/sample_pubsub_test_integration.py 
import base64
import os
import subprocess
import uuid

import requests
from requests.packages.urllib3.util.retry import Retry


def test_print_name():
    name = str(uuid.uuid4())
    port = 8088  # Each running framework instance needs a unique port

    encoded_name = base64.b64encode(name.encode('utf-8')).decode('utf-8')
    pubsub_message = {
        'data': {'data': encoded_name}
    }

    process = subprocess.Popen(
      [
        'functions-framework',
        '--target', 'hello_pubsub',
        '--signature-type', 'event',
        '--port', str(port)
      ],
      cwd=os.path.dirname(__file__),
      stdout=subprocess.PIPE
    )

    # Send HTTP request simulating Pub/Sub message
    # (GCF translates Pub/Sub messages to HTTP requests internally)
    url = f'http://localhost:{port}/'

    retry_policy = Retry(total=6, backoff_factor=1)
    retry_adapter = requests.adapters.HTTPAdapter(
      max_retries=retry_policy)

    session = requests.Session()
    session.mount(url, retry_adapter)

    response = session.post(url, json=pubsub_message)

    assert response.status_code == 200

    # Stop the functions framework process
    process.kill()
    process.wait()
    out, err = process.communicate()

    print(out, err, response.content)

    assert f'Hello {name}!' in str(out)

Java

functions/helloworld/hello-pubsub/src/test/java/functions/ExampleIntegrationTest.java 

import static com.google.common.truth.Truth.assertThat;

import com.google.gson.Gson;
import io.github.resilience4j.core.IntervalFunction;
import io.github.resilience4j.retry.Retry;
import io.github.resilience4j.retry.RetryConfig;
import io.github.resilience4j.retry.RetryRegistry;
import io.vavr.CheckedRunnable;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.net.URI;
import java.nio.charset.StandardCharsets;
import java.util.Base64;
import java.util.Map;
import java.util.UUID;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.conn.HttpHostConnectException;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.HttpClientBuilder;
import org.junit.AfterClass;
import org.junit.BeforeClass;
import org.junit.Test;

public class ExampleIntegrationTest {
  // Root URL pointing to the locally hosted function
  // The Functions Framework Maven plugin lets us run a function locally
  private static final String BASE_URL = "http://localhost:8080";

  private static Process emulatorProcess = null;
  private static HttpClient client = HttpClientBuilder.create().build();
  private static final Gson gson = new Gson();

  @BeforeClass
  public static void setUp() throws IOException {
    // Get the sample's base directory (the one containing a pom.xml file)
    String baseDir = System.getProperty("basedir");

    // Emulate the function locally by running the Functions Framework Maven plugin
    emulatorProcess = new ProcessBuilder()
        .command("mvn", "function:run")
        .directory(new File(baseDir))
        .start();
  }

  @AfterClass
  public static void tearDown() {
    // Terminate the running Functions Framework Maven plugin process (if it's still running)
    if (emulatorProcess.isAlive()) {
      emulatorProcess.destroy();
    }
  }

  @Test
  public void helloPubSub_shouldRunWithFunctionsFramework() throws Throwable {
    String functionUrl = BASE_URL + "/helloPubsub"; // URL to your locally-running function

    // Initialize constants
    String name = UUID.randomUUID().toString();
    String nameBase64 = Base64.getEncoder().encodeToString(name.getBytes(StandardCharsets.UTF_8));

    String jsonStr = gson.toJson(Map.of("data", Map.of("data", nameBase64)));

    HttpPost postRequest =  new HttpPost(URI.create(functionUrl));
    postRequest.setEntity(new StringEntity(jsonStr));

    // The Functions Framework Maven plugin process takes time to start up
    // Use resilience4j to retry the test HTTP request until the plugin responds
    RetryRegistry registry = RetryRegistry.of(RetryConfig.custom()
        .maxAttempts(8)
        .retryExceptions(HttpHostConnectException.class)
        .intervalFunction(IntervalFunction.ofExponentialBackoff(200, 2))
        .build());
    Retry retry = registry.retry("my");

    // Perform the request-retry process
    CheckedRunnable retriableFunc = Retry.decorateCheckedRunnable(
        retry, () -> client.execute(postRequest));
    retriableFunc.run();

    // Get Functions Framework plugin process' stdout
    InputStream stdoutStream = emulatorProcess.getErrorStream();
    ByteArrayOutputStream stdoutBytes = new ByteArrayOutputStream();
    stdoutBytes.write(stdoutStream.readNBytes(stdoutStream.available()));

    // Verify desired name value is present
    assertThat(stdoutBytes.toString(StandardCharsets.UTF_8)).contains(
        String.format("Hello %s!", name));
  }
}

You can run the integration tests for this function as follows:

Node.js 

mocha test/sample.integration.pubsub.test.js --exit

Python 

pytest sample_pubsub_test_integration.py

Java 

mvn clean verify -Dtest=ExampleIntegrationTest

System tests

Here are system tests for this function:

Node.js

functions/helloworld/test/sample.system.pubsub.test.js 
const childProcess = require('child_process');
const assert = require('assert');
const uuid = require('uuid');
const {PubSub} = require('@google-cloud/pubsub');
const moment = require('moment');
const promiseRetry = require('promise-retry');

const pubsub = new PubSub();
const topicName = process.env.FUNCTIONS_TOPIC;
const baseCmd = 'gcloud functions';

describe('system tests', () => {
  it('helloPubSub: should print a name', async () => {
    const name = uuid.v4();

    // Subtract time to work-around local-GCF clock difference
    const startTime = moment().subtract(4, 'minutes').toISOString();

    // Publish to pub/sub topic
    const topic = pubsub.topic(topicName);
    await topic.publish(Buffer.from(name));

    // Wait for logs to become consistent
    await promiseRetry((retry) => {
      const logs = childProcess
        .execSync(`${baseCmd} logs read helloPubSub --start-time ${startTime}`)
        .toString();

      try {
        assert.ok(logs.includes(`Hello, ${name}!`));
      } catch (err) {
        retry(err);
      }
    });
  });

Python

functions/helloworld/sample_pubsub_test_system.py 
from datetime import datetime
from os import getenv
import subprocess
import time
import uuid

from google.cloud import pubsub_v1
import pytest

PROJECT = getenv('GCP_PROJECT')
TOPIC = getenv('TOPIC')

assert PROJECT is not None
assert TOPIC is not None


@pytest.fixture(scope='module')
def publisher_client():
    yield pubsub_v1.PublisherClient()


def test_print_name(publisher_client):
    start_time = datetime.utcnow().isoformat()
    topic_path = publisher_client.topic_path(PROJECT, TOPIC)

    # Publish the message
    name = uuid.uuid4()
    data = str(name).encode('utf-8')
    publisher_client.publish(topic_path, data=data).result()

    # Wait for logs to become consistent
    time.sleep(15)

    # Check logs after a delay
    log_process = subprocess.Popen([
        'gcloud',
        'alpha',
        'functions',
        'logs',
        'read',
        'hello_pubsub',
        '--start-time',
        start_time
    ], stdout=subprocess.PIPE)
    logs = str(log_process.communicate()[0])
    assert 'Hello {}!'.format(name) in logs

Go

functions/helloworld/hello_pubsub_system_test.go 

package helloworld

import (
	"context"
	"log"
	"os"
	"os/exec"
	"strings"
	"testing"
	"time"

	"cloud.google.com/go/pubsub"
	"github.com/gobuffalo/uuid"
)

func TestHelloPubSubSystem(t *testing.T) {
	ctx := context.Background()

	topicName := os.Getenv("FUNCTIONS_TOPIC")
	projectID := os.Getenv("GCP_PROJECT")

	startTime := time.Now().UTC().Format(time.RFC3339)

	// Create the Pub/Sub client and topic.
	client, err := pubsub.NewClient(ctx, projectID)
	if err != nil {
		log.Fatal(err)
	}
	topic := client.Topic(topicName)

	// Publish a message with a random string to verify.
	// We use a random string to make sure the function is logging the correct
	// message for this test invocation.
	u := uuid.Must(uuid.NewV4())
	msg := &pubsub.Message{
		Data: []byte(u.String()),
	}
	topic.Publish(ctx, msg).Get(ctx)

	// Wait for logs to be consistent.
	time.Sleep(20 * time.Second)

	// Check logs after a delay.
	cmd := exec.Command("gcloud", "alpha", "functions", "logs", "read", "HelloPubSub", "--start-time", startTime)
	out, err := cmd.CombinedOutput()
	if err != nil {
		t.Fatalf("exec.Command: %v", err)
	}
	if got := string(out); !strings.Contains(got, u.String()) {
		t.Errorf("HelloPubSub got %q, want to contain %q", got, u.String())
	}
}

Java

functions/helloworld/hello-pubsub/src/test/java/functions/ExampleSystemTest.java 
import static com.google.common.truth.Truth.assertThat;

import com.google.api.gax.paging.Page;
import com.google.cloud.logging.LogEntry;
import com.google.cloud.logging.Logging;
import com.google.cloud.logging.LoggingOptions;
import com.google.cloud.pubsub.v1.Publisher;
import com.google.protobuf.ByteString;
import com.google.pubsub.v1.ProjectTopicName;
import com.google.pubsub.v1.PubsubMessage;
import io.github.resilience4j.core.IntervalFunction;
import io.github.resilience4j.retry.Retry;
import io.github.resilience4j.retry.RetryConfig;
import io.github.resilience4j.retry.RetryRegistry;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.time.Duration;
import java.time.Instant;
import java.time.format.DateTimeFormatter;
import java.util.UUID;
import java.util.stream.Collectors;
import java.util.stream.StreamSupport;
import org.junit.BeforeClass;
import org.junit.Test;

public class ExampleSystemTest {

  // TODO<developer>: set these values (as environment variables)
  private static final String PROJECT_ID = System.getenv("GCP_PROJECT");
  private static final String TOPIC_NAME = System.getenv("FUNCTIONS_SYSTEM_TEST_TOPIC");
  private static final String FUNCTION_DEPLOYED_NAME = "HelloPubSub";

  private static Logging loggingClient;

  private static Publisher publisher;

  private HelloPubSub sampleUnderTest;

  @BeforeClass
  public static void setUp() throws IOException {
    loggingClient = LoggingOptions.getDefaultInstance().getService();
    publisher = Publisher.newBuilder(
        ProjectTopicName.of(PROJECT_ID, TOPIC_NAME)).build();
  }

  private static String getLogEntriesAsString(String startTimestamp) {
    // Construct Stackdriver logging filter
    // See this page for more info: https://cloud.google.com/logging/docs/view/advanced-queries
    String filter = "resource.type=\"cloud_function\""
        + " AND severity=INFO"
        + " AND resource.labels.function_name=" + FUNCTION_DEPLOYED_NAME
        + String.format(" AND timestamp>=\"%s\"", startTimestamp);

    // Get Stackdriver logging entries
    Page<LogEntry> logEntries =
        loggingClient.listLogEntries(
            Logging.EntryListOption.filter(filter),
            Logging.EntryListOption.sortOrder(
                Logging.SortingField.TIMESTAMP, Logging.SortingOrder.DESCENDING)
        );

    // Serialize Stackdriver logging entries + collect them into a single string
    String logsConcat = StreamSupport.stream(logEntries.getValues().spliterator(), false)
        .map((x) -> x.toString())
        .collect(Collectors.joining("%n"));

    return logsConcat;
  }

  @Test
  public void helloPubSub_shouldRunOnGcf() throws Exception {
    String name = UUID.randomUUID().toString();

    // Subtract time to work-around local-GCF clock difference
    Instant startInstant = Instant.now().minus(Duration.ofMinutes(4));
    String startTimestamp = DateTimeFormatter.ISO_INSTANT.format(startInstant);

    // Publish to pub/sub topic
    ByteString byteStr = ByteString.copyFrom(name, StandardCharsets.UTF_8);
    PubsubMessage pubsubApiMessage = PubsubMessage.newBuilder().setData(byteStr).build();
    publisher.publish(pubsubApiMessage).get();

    // Keep retrying until the logs contain the desired invocation's log entry
    // (If the invocation failed, the retry process will eventually time out)
    RetryRegistry registry = RetryRegistry.of(RetryConfig.custom()
        .maxAttempts(8)
        .intervalFunction(IntervalFunction.ofExponentialBackoff(1000, 2))
        .retryOnResult(s -> !s.toString().contains(name))
        .build());
    Retry retry = registry.retry(name);
    String logEntry = Retry
        .decorateFunction(retry, ExampleSystemTest::getLogEntriesAsString)
        .apply(startTimestamp);

    // Perform final assertion (to make sure we fail on timeout)
    assertThat(logEntry).contains(name);
  }
}

Run the system tests by following these instructions:

  1. In your Cloud project, select a Pub/Sub topic to subscribe to. If you provide the name of a Pub/Sub topic that does not exist, it is created automatically.

  2. Next, deploy your functions using the following command:

    Node.js 

    gcloud functions deploy helloPubSub \
--runtime nodejs10 \
    --trigger-topic YOUR_PUBSUB_TOPIC
    You can use the following values for the --runtime flag to specify your preferred Node.js version:
    • nodejs10
    • nodejs12

    Python 

    gcloud functions deploy hello_pubsub \
--runtime python37 \
    --trigger-topic YOUR_PUBSUB_TOPIC
    You can use the following values for the --runtime flag to specify your preferred Python version:
    • python37
    • python38

    Go 

    gcloud functions deploy HelloPubSub \
--runtime go111 \
    --trigger-topic YOUR_PUBSUB_TOPIC
    You can use the following values for the --runtime flag to specify your preferred Go version:
    • go111
    • go113

    Java 

    gcloud functions deploy java-hello-pubsub \
--entry-point functions.HelloPubSub \
--runtime java11 \
--memory 512MB \
    --trigger-topic YOUR_PUBSUB_TOPIC

    where YOUR_PUBSUB_TOPIC is the name of the Pub/Sub topic you want your functions to subscribe to.

  3. Run the system tests with the following command:

    Node.js 

    export FUNCTIONS_TOPIC=YOUR_PUBSUB_TOPIC
mocha test/sample.system.pubsub.test.js --exit

    Python 

    export FUNCTIONS_TOPIC=YOUR_PUBSUB_TOPIC
pytest sample_pubsub_test_system.py

    Go 

    export FUNCTIONS_TOPIC=YOUR_PUBSUB_TOPIC
go test -v ./hello_pubsub_system_test.go

    Java 

    export FUNCTIONS_TOPIC=YOUR_PUBSUB_TOPIC
mvn clean verify

    where YOUR_PUBSUB_TOPIC is the name of the Pub/Sub topic you want your functions to subscribe to.

Storage-triggered functions

Tests for storage-triggered functions are similar in structure to their Pub/Sub-triggered counterparts. Like Pub/Sub-triggered function tests, storage-triggered function tests are structured differently depending on where the tested function is hosted.

Here is an example of a storage-triggered function:

Node.js

functions/helloworld/index.js 
/**
 * Generic background Cloud Function to be triggered by Cloud Storage.
 *
 * @param {object} file The Cloud Storage file metadata.
 * @param {object} context The event metadata.
 */
exports.helloGCS = (file, context) => {
  console.log(`  Event: ${context.eventId}`);
  console.log(`  Event Type: ${context.eventType}`);
  console.log(`  Bucket: ${file.bucket}`);
  console.log(`  File: ${file.name}`);
  console.log(`  Metageneration: ${file.metageneration}`);
  console.log(`  Created: ${file.timeCreated}`);
  console.log(`  Updated: ${file.updated}`);
};

Python

functions/helloworld/main.py 
def hello_gcs(event, context):
    """Background Cloud Function to be triggered by Cloud Storage.
       This generic function logs relevant data when a file is changed.

    Args:
        event (dict):  The dictionary with data specific to this type of event.
                       The `data` field contains a description of the event in
                       the Cloud Storage `object` format described here:
                       https://cloud.google.com/storage/docs/json_api/v1/objects#resource
        context (google.cloud.functions.Context): Metadata of triggering event.
    Returns:
        None; the output is written to Stackdriver Logging
    """

    print('Event ID: {}'.format(context.event_id))
    print('Event type: {}'.format(context.event_type))
    print('Bucket: {}'.format(event['bucket']))
    print('File: {}'.format(event['name']))
    print('Metageneration: {}'.format(event['metageneration']))
    print('Created: {}'.format(event['timeCreated']))
    print('Updated: {}'.format(event['updated']))

Go

functions/helloworld/hello_cloud_storage.go 

// Package helloworld provides a set of Cloud Functions samples.
package helloworld

import (
	"context"
	"fmt"
	"log"
	"time"

	"cloud.google.com/go/functions/metadata"
)

// GCSEvent is the payload of a GCS event.
type GCSEvent struct {
	Kind                    string                 `json:"kind"`
	ID                      string                 `json:"id"`
	SelfLink                string                 `json:"selfLink"`
	Name                    string                 `json:"name"`
	Bucket                  string                 `json:"bucket"`
	Generation              string                 `json:"generation"`
	Metageneration          string                 `json:"metageneration"`
	ContentType             string                 `json:"contentType"`
	TimeCreated             time.Time              `json:"timeCreated"`
	Updated                 time.Time              `json:"updated"`
	TemporaryHold           bool                   `json:"temporaryHold"`
	EventBasedHold          bool                   `json:"eventBasedHold"`
	RetentionExpirationTime time.Time              `json:"retentionExpirationTime"`
	StorageClass            string                 `json:"storageClass"`
	TimeStorageClassUpdated time.Time              `json:"timeStorageClassUpdated"`
	Size                    string                 `json:"size"`
	MD5Hash                 string                 `json:"md5Hash"`
	MediaLink               string                 `json:"mediaLink"`
	ContentEncoding         string                 `json:"contentEncoding"`
	ContentDisposition      string                 `json:"contentDisposition"`
	CacheControl            string                 `json:"cacheControl"`
	Metadata                map[string]interface{} `json:"metadata"`
	CRC32C                  string                 `json:"crc32c"`
	ComponentCount          int                    `json:"componentCount"`
	Etag                    string                 `json:"etag"`
	CustomerEncryption      struct {
		EncryptionAlgorithm string `json:"encryptionAlgorithm"`
		KeySha256           string `json:"keySha256"`
	}
	KMSKeyName    string `json:"kmsKeyName"`
	ResourceState string `json:"resourceState"`
}

// HelloGCS consumes a GCS event.
func HelloGCS(ctx context.Context, e GCSEvent) error {
	meta, err := metadata.FromContext(ctx)
	if err != nil {
		return fmt.Errorf("metadata.FromContext: %v", err)
	}
	log.Printf("Event ID: %v\n", meta.EventID)
	log.Printf("Event type: %v\n", meta.EventType)
	log.Printf("Bucket: %v\n", e.Bucket)
	log.Printf("File: %v\n", e.Name)
	log.Printf("Metageneration: %v\n", e.Metageneration)
	log.Printf("Created: %v\n", e.TimeCreated)
	log.Printf("Updated: %v\n", e.Updated)
	return nil
}

Java

functions/helloworld/hello-gcs/src/main/java/functions/HelloGcs.java 
import com.google.cloud.functions.BackgroundFunction;
import com.google.cloud.functions.Context;
import functions.eventpojos.GcsEvent;
import java.util.logging.Logger;

public class HelloGcs implements BackgroundFunction<GcsEvent> {
  private static final Logger logger = Logger.getLogger(HelloGcs.class.getName());

  @Override
  public void accept(GcsEvent event, Context context) {
    logger.info("Event: " + context.eventId());
    logger.info("Event Type: " + context.eventType());
    logger.info("Bucket: " + event.getBucket());
    logger.info("File: " + event.getName());
    logger.info("Metageneration: " + event.getMetageneration());
    logger.info("Created: " + event.getTimeCreated());
    logger.info("Updated: " + event.getUpdated());
  }
}

Unit tests

Here are unit tests for the storage-triggered function above:

Node.js

functions/helloworld/test/sample.unit.storage.test.js 
const assert = require('assert');
const uuid = require('uuid');
const sinon = require('sinon');

const {helloGCS} = require('..');

const stubConsole = function () {
  sinon.stub(console, `error`);
  sinon.stub(console, `log`);
};

const restoreConsole = function () {
  console.log.restore();
  console.error.restore();
};

beforeEach(stubConsole);
afterEach(restoreConsole);

it('helloGCS: should print out event', () => {
  // Initialize mocks
  const filename = uuid.v4();
  const eventType = 'google.storage.object.finalize';
  const event = {
    name: filename,
    resourceState: 'exists',
    metageneration: '1',
  };
  const context = {
    eventId: 'g1bb3r1sh',
    eventType: eventType
  }

  // Call tested function and verify its behavior
  helloGCS(event, context);
  assert.ok(console.log.calledWith(`  File: ${filename}`));
  assert.ok(console.log.calledWith(`  Event Type: ${eventType}`));
});

Python

functions/helloworld/sample_storage_test.py 
import mock

import main


def test_print(capsys):
    name = 'test'
    event = {
        'bucket': 'some-bucket',
        'name': name,
        'metageneration': 'some-metageneration',
        'timeCreated': '0',
        'updated': '0'
    }

    context = mock.MagicMock()
    context.event_id = 'some-id'
    context.event_type = 'gcs-event'

    # Call tested function
    main.hello_gcs(event, context)
    out, err = capsys.readouterr()
    assert 'File: {}\n'.format(name) in out

Go

functions/helloworld/hello_cloud_storage_test.go 
package helloworld

import (
	"context"
	"io/ioutil"
	"log"
	"os"
	"strings"
	"testing"

	"cloud.google.com/go/functions/metadata"
)

func TestHelloGCS(t *testing.T) {
	r, w, _ := os.Pipe()
	log.SetOutput(w)
	originalFlags := log.Flags()
	log.SetFlags(log.Flags() &^ (log.Ldate | log.Ltime))

	name := "hello_gcs.txt"
	e := GCSEvent{
		Name: name,
	}
	meta := &metadata.Metadata{
		EventID: "event ID",
	}
	ctx := metadata.NewContext(context.Background(), meta)

	HelloGCS(ctx, e)

	w.Close()
	log.SetOutput(os.Stderr)
	log.SetFlags(originalFlags)

	out, err := ioutil.ReadAll(r)
	if err != nil {
		t.Fatalf("ReadAll: %v", err)
	}

	got := string(out)
	wants := []string{
		"File: " + name,
		"Event ID: " + meta.EventID,
	}
	for _, want := range wants {
		if !strings.Contains(got, want) {
			t.Errorf("HelloGCS(%v) = %q, want to contain %q", e, got, want)
		}
	}
}

Java

functions/helloworld/hello-gcs/src/test/java/functions/HelloGcsTest.java 
import static com.google.common.truth.Truth.assertThat;

import com.google.common.testing.TestLogHandler;
import functions.eventpojos.GcsEvent;
import functions.eventpojos.MockContext;
import java.util.logging.Logger;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

/**
 * Unit tests for main.java.com.example.functions.helloworld.HelloGcs.
 */
public class HelloGcsTest {
  private static final TestLogHandler LOG_HANDLER = new TestLogHandler();
  private static final Logger logger = Logger.getLogger(HelloGcs.class.getName());

  @Before
  public void beforeTest() throws Exception {
    logger.addHandler(LOG_HANDLER);
  }

  @After
  public void afterTest() {
    LOG_HANDLER.clear();
  }

  @Test
  public void helloGcs_shouldPrintFileName() {
    GcsEvent event = new GcsEvent();
    event.setName("foo.txt");

    MockContext context = new MockContext();
    context.eventType = "google.storage.object.finalize";

    new HelloGcs().accept(event, context);

    String message = LOG_HANDLER.getStoredLogRecords().get(3).getMessage();
    assertThat(message).contains("File: foo.txt");
  }
}

Run the unit tests with the following command:

Node.js 

mocha test/sample.unit.storage.test.js --exit

Python 

pytest sample_storage_test.py

Go 

go test -v ./hello_cloud_storage_test.go

Java 

mvn clean verify

Integration tests

Here are integration tests for the storage-triggered function above:

Node.js

functions/helloworld/test/sample.integration.storage.test.js 
const assert = require('assert');
const execPromise = require('child-process-promise').exec;
const path = require('path');
const uuid = require('uuid');

const requestRetry = require('requestretry');
const cwd = path.join(__dirname, '..');

  it('helloGCSGeneric: should print GCS event', async () => {
    const filename = uuid.v4(); // Use a unique filename to avoid conflicts
    const PORT = 9000; // Each running framework instance needs a unique port

    const eventType = 'google.storage.object.finalize';

    const data = {
      data: {
        name: filename,
        resourceState: 'exists',
        metageneration: '1',
      },
      context: {
        eventType: eventType
      }
    };

    // Run the functions-framework instance to host functions locally
    //   exec's 'timeout' param won't kill children of "shim" /bin/sh process
    //   Workaround: include "& sleep <TIMEOUT>; kill $!" in executed command
    const proc = execPromise(
      `functions-framework --target=helloGCS --signature-type=event --port=${PORT} & sleep 1; kill $!`,
      {shell: true, cwd}
    );

    // Send HTTP request simulating GCS change notification
    // (GCF translates GCS notifications to HTTP requests internally)
    const response = await requestRetry({
      url: `http://localhost:${PORT}/`,
      method: 'POST',
      body: data,
      retryDelay: 200,
      json: true,
    });

    assert.strictEqual(response.statusCode, 204);

    // Wait for functions-framework process to exit
    const {stdout} = await proc;
    assert.ok(stdout.includes(`File: ${filename}`));
    assert.ok(stdout.includes(`Event Type: ${eventType}`));
  });
});

Java

functions/helloworld/hello-gcs/src/test/java/functions/ExampleIntegrationTest.java 

import static com.google.common.truth.Truth.assertThat;

import com.google.gson.Gson;
import io.github.resilience4j.core.IntervalFunction;
import io.github.resilience4j.retry.Retry;
import io.github.resilience4j.retry.RetryConfig;
import io.github.resilience4j.retry.RetryRegistry;
import io.vavr.CheckedRunnable;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.net.URI;
import java.nio.charset.StandardCharsets;
import java.util.Map;
import java.util.UUID;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.conn.HttpHostConnectException;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.HttpClientBuilder;
import org.junit.AfterClass;
import org.junit.BeforeClass;
import org.junit.Test;

public class ExampleIntegrationTest {
  // Root URL pointing to the locally hosted function
  // The Functions Framework Maven plugin lets us run a function locally
  private static final String BASE_URL = "http://localhost:8080";

  private static Process emulatorProcess = null;
  private static final HttpClient client = HttpClientBuilder.create().build();
  private static final Gson gson = new Gson();

  @BeforeClass
  public static void setUp() throws IOException {
    // Get the sample's base directory (the one containing a pom.xml file)
    String baseDir = System.getProperty("basedir");

    // Emulate the function locally by running the Functions Framework Maven plugin
    emulatorProcess = new ProcessBuilder()
        .command("mvn", "function:run")
        .directory(new File(baseDir))
        .start();
  }

  @AfterClass
  public static void tearDown() {
    // Terminate the running Functions Framework Maven plugin process (if it's still running)
    if (emulatorProcess.isAlive()) {
      emulatorProcess.destroy();
    }
  }

  @Test
  public void helloGcs_shouldRunWithFunctionsFramework() throws Throwable {
    String functionUrl = BASE_URL + "/helloGcs"; // URL to your locally-running function

    // Initialize constants
    String name = UUID.randomUUID().toString();
    String jsonStr = gson.toJson(Map.of(
        "data", Map.of(
            "name", name, "resourceState", "exists", "metageneration", 1),
        "context", Map.of(
            "eventType", "google.storage.object.finalize")
    ));

    HttpPost postRequest =  new HttpPost(URI.create(functionUrl));
    postRequest.setEntity(new StringEntity(jsonStr));

    // The Functions Framework Maven plugin process takes time to start up
    // Use resilience4j to retry the test HTTP request until the plugin responds
    RetryRegistry registry = RetryRegistry.of(RetryConfig.custom()
        .maxAttempts(8)
        .retryExceptions(HttpHostConnectException.class)
        .intervalFunction(IntervalFunction.ofExponentialBackoff(200, 2))
        .build());
    Retry retry = registry.retry("my");

    // Perform the request-retry process
    CheckedRunnable retriableFunc = Retry.decorateCheckedRunnable(
        retry, () -> client.execute(postRequest));
    retriableFunc.run();

    // Get Functions Framework plugin process' stdout
    InputStream stdoutStream = emulatorProcess.getErrorStream();
    ByteArrayOutputStream stdoutBytes = new ByteArrayOutputStream();
    stdoutBytes.write(stdoutStream.readNBytes(stdoutStream.available()));

    // Verify desired name value is present
    assertThat(stdoutBytes.toString(StandardCharsets.UTF_8)).contains(
        String.format("File: %s", name));
  }
}

You can run the integration tests for this function as follows:

Node.js 

mocha test/sample.integration.storage.test.js --exit

Java 

mvn clean verify -Dtest=ExampleIntegrationTest

System tests

These are the system tests for the storage-triggered function above:

Node.js

functions/helloworld/test/sample.system.storage.test.js 
const {Storage} = require('@google-cloud/storage');
const storage = new Storage();
const uuid = require('uuid');
const assert = require('assert');
const path = require('path');
const childProcess = require('child_process');
const moment = require('moment');
const promiseRetry = require('promise-retry');

// Use unique GCS filename to avoid conflicts between concurrent test runs
const gcsFileName = `test-${uuid.v4()}.txt`;

const localFileName = 'test.txt';
const bucketName = process.env.FUNCTIONS_DELETABLE_BUCKET;
const bucket = storage.bucket(bucketName);
const baseCmd = 'gcloud functions';

describe('system tests', () => {
  it('helloGCS: should print event', async () => {
    // Subtract time to work-around local-GCF clock difference
    const startTime = moment().subtract(2, 'minutes').toISOString();

    // Upload file
    const filepath = path.join(__dirname, localFileName);
    await bucket.upload(filepath, {
      destination: gcsFileName,
    });

    // Wait for logs to become consistent
    await promiseRetry((retry) => {
      const logs = childProcess
        .execSync(`${baseCmd} logs read helloGCS --start-time ${startTime}`)
        .toString();

      try {
        assert.ok(logs.includes(`Filename: ${gcsFileName}`));
        assert.ok(logs.includes(`Event Type: google.storage.object.finalize`));
      } catch (err) {
        retry(err);
      }
    });
  });

Python

functions/helloworld/sample_storage_test_system.py 
from datetime import datetime
from os import getenv, path
import subprocess
import time
import uuid

from google.cloud import storage
import pytest

PROJECT = getenv('GCP_PROJECT')
BUCKET = getenv('BUCKET')

assert PROJECT is not None
assert BUCKET is not None


@pytest.fixture(scope='module')
def storage_client():
    yield storage.Client()


@pytest.fixture(scope='module')
def bucket_object(storage_client):
    bucket_object = storage_client.get_bucket(BUCKET)
    yield bucket_object


@pytest.fixture(scope='module')
def uploaded_file(bucket_object):
    name = 'test-{}.txt'.format(str(uuid.uuid4()))
    blob = bucket_object.blob(name)

    test_dir = path.dirname(path.abspath(__file__))
    blob.upload_from_filename(path.join(test_dir, 'test.txt'))
    yield name
    blob.delete()


def test_hello_gcs(uploaded_file):
    start_time = datetime.utcnow().isoformat()
    time.sleep(10)  # Wait for logs to become consistent

    log_process = subprocess.Popen([
        'gcloud',
        'alpha',
        'functions',
        'logs',
        'read',
        'hello_gcs_generic',
        '--start-time',
        start_time
    ], stdout=subprocess.PIPE)
    logs = str(log_process.communicate()[0])
    assert uploaded_file in logs

Go

functions/helloworld/hello_cloud_storage_system_test.go 

package helloworld

import (
	"context"
	"fmt"
	"os"
	"os/exec"
	"strings"
	"testing"
	"time"

	"cloud.google.com/go/storage"
)

func TestHelloGCSSystem(t *testing.T) {
	ctx := context.Background()
	bucketName := os.Getenv("BUCKET_NAME")

	client, err := storage.NewClient(ctx)
	if err != nil {
		t.Fatalf("storage.NewClient: %v", err)
	}

	// Create a file.
	startTime := time.Now().UTC().Format(time.RFC3339)
	oh := client.Bucket(bucketName).Object("TestHelloGCSSystem")
	w := oh.NewWriter(ctx)
	fmt.Fprintf(w, "Content of the file")
	w.Close()

	// Wait for logs to be consistent.
	time.Sleep(20 * time.Second)

	// Check logs.
	want := "created"
	if got := readLogs(t, startTime); !strings.Contains(got, want) {
		t.Errorf("HelloGCS logged %q, want to contain %q", got, want)
	}

	// Modify the file.
	startTime = time.Now().UTC().Format(time.RFC3339)
	_, err = oh.Update(ctx, storage.ObjectAttrsToUpdate{
		Metadata: map[string]string{"Content-Type": "text/html"},
	})
	if err != nil {
		t.Errorf("Update: %v", err)
	}

	// Wait for logs to be consistent.
	time.Sleep(20 * time.Second)

	// Check logs.
	want = "updated"
	if got := readLogs(t, startTime); !strings.Contains(got, want) {
		t.Errorf("HelloGCS logged %q, want to contain %q", got, want)
	}

	// Delete the file.
	startTime = time.Now().UTC().Format(time.RFC3339)
	if err := oh.Delete(ctx); err != nil {
		t.Errorf("Delete: %v", err)
	}

	// Wait for logs to be consistent.
	time.Sleep(20 * time.Second)

	// Check logs.
	want = "deleted"
	if got := readLogs(t, startTime); !strings.Contains(got, want) {
		t.Errorf("HelloGCS logged %q, want to contain %q", got, want)
	}
}

func readLogs(t *testing.T, startTime string) string {
	t.Helper()
	cmd := exec.Command("gcloud", "alpha", "functions", "logs", "read", "HelloGCS", "--start-time", startTime)
	got, err := cmd.CombinedOutput()
	if err != nil {
		t.Fatalf("exec.Command: %v", err)
	}
	return string(got)
}

Java

functions/helloworld/hello-gcs/src/test/java/functions/ExampleSystemTest.java 
import static com.google.common.truth.Truth.assertThat;

import com.google.api.gax.paging.Page;
import com.google.cloud.logging.LogEntry;
import com.google.cloud.logging.Logging;
import com.google.cloud.logging.LoggingOptions;
import com.google.cloud.storage.BlobId;
import com.google.cloud.storage.BlobInfo;
import com.google.cloud.storage.Storage;
import com.google.cloud.storage.StorageOptions;
import io.github.resilience4j.core.IntervalFunction;
import io.github.resilience4j.retry.Retry;
import io.github.resilience4j.retry.RetryConfig;
import io.github.resilience4j.retry.RetryRegistry;
import java.io.IOException;
import java.time.Duration;
import java.time.Instant;
import java.time.format.DateTimeFormatter;
import java.util.UUID;
import java.util.stream.Collectors;
import java.util.stream.StreamSupport;
import org.junit.BeforeClass;
import org.junit.Test;

public class ExampleSystemTest {

  // TODO<developer>: set these values (as environment variables)
  private static final String PROJECT_ID = System.getenv("GCP_PROJECT");
  private static final String FUNCTIONS_BUCKET = System.getenv("FUNCTIONS_BUCKET");
  private static final String FUNCTION_DEPLOYED_NAME = "HelloGcs";
  private static final Storage STORAGE = StorageOptions.getDefaultInstance().getService();

  private static Logging loggingClient;

  private HelloGcs sampleUnderTest;

  @BeforeClass
  public static void setUp() throws IOException {
    loggingClient = LoggingOptions.getDefaultInstance().getService();
  }

  private static String getLogEntriesAsString(String startTimestamp) {
    // Construct Stackdriver logging filter
    // See this page for more info: https://cloud.google.com/logging/docs/view/advanced-queries
    String filter = "resource.type=\"cloud_function\""
        + " AND severity=INFO"
        + " AND resource.labels.function_name=" + FUNCTION_DEPLOYED_NAME
        + String.format(" AND timestamp>=\"%s\"", startTimestamp);

    // Get Stackdriver logging entries
    Page<LogEntry> logEntries =
        loggingClient.listLogEntries(
            Logging.EntryListOption.filter(filter),
            Logging.EntryListOption.sortOrder(
                Logging.SortingField.TIMESTAMP, Logging.SortingOrder.DESCENDING)
        );

    // Serialize Stackdriver logging entries + collect them into a single string
    String logsConcat = StreamSupport.stream(logEntries.getValues().spliterator(), false)
        .map((x) -> x.toString())
        .collect(Collectors.joining("%n"));

    return logsConcat;
  }

  @Test
  public void helloGcs_shouldRunOnGcf() {
    String filename = String.format("test-%s.txt", UUID.randomUUID());

    // Subtract time to work-around local-GCF clock difference
    Instant startInstant = Instant.now().minus(Duration.ofMinutes(4));
    String startTimestamp = DateTimeFormatter.ISO_INSTANT.format(startInstant);

    // Upload a file to Cloud Storage
    BlobInfo blobInfo = BlobInfo.newBuilder(BlobId.of(FUNCTIONS_BUCKET, filename)).build();
    STORAGE.create(blobInfo);

    // Keep retrying until the logs contain the desired invocation's log entry
    // (If the invocation failed, the retry process will eventually time out)
    String expected = String.format("File: %s", filename);
    RetryRegistry registry = RetryRegistry.of(RetryConfig.custom()
        .maxAttempts(8)
        .intervalFunction(IntervalFunction.ofExponentialBackoff(1000, 2))
        .retryOnResult(s -> !s.toString().contains(expected))
        .build());
    Retry retry = registry.retry(filename);
    String logEntry = Retry
        .decorateFunction(retry, ExampleSystemTest::getLogEntriesAsString)
        .apply(startTimestamp);

    // Perform final assertion (to make sure we fail on timeout)
    assertThat(logEntry).contains(filename);
  }
}

Deploy your function with the following command:

Node.js 

gcloud functions deploy helloGCS \
--runtime nodejs10 \
--trigger-bucket YOUR_GCS_BUCKET_NAME
You can use the following values for the --runtime flag to specify your preferred Node.js version:
  • nodejs10
  • nodejs12

Python 

gcloud functions deploy hello_gcs \
--runtime python37 \
--trigger-bucket YOUR_GCS_BUCKET_NAME
You can use the following values for the --runtime flag to specify your preferred Python version:
  • python37
  • python38

Go 

gcloud functions deploy HelloGCS \
--runtime go111 \
--trigger-bucket YOUR_GCS_BUCKET_NAME
You can use the following values for the --runtime flag to specify your preferred Go version:
  • go111
  • go113

Java 

gcloud functions deploy java-hello-gcs \
--entry-point functions.HelloGcs \
--runtime java11 \
--memory 512MB \
--trigger-bucket YOUR_GCS_BUCKET_NAME

where YOUR_GCS_BUCKET_NAME is the Cloud Storage bucket you want to monitor. Note that this must reference a bucket that exists in the same Cloud project that the function is deployed to.

Run system tests with the following commands:

Node.js 

export BUCKET_NAME=YOUR_GCS_BUCKET_NAME
mocha test/sample.system.storage.test.js --exit

Python 

export BUCKET_NAME=YOUR_GCS_BUCKET_NAME
pytest sample_storage_test_system.py

Go 

export BUCKET_NAME=YOUR_GCS_BUCKET_NAME
go test -v ./hello_cloud_storage_system_test.go

Java 

mvn clean verify