How to automate integration testing of Java functions?

For Java functions, you can use JUnit, Mockito and Cloud Functions Framework to perform automated integration testing. The steps are as follows: Install dependencies: junit, mockito-core, google-cloud-functions-framework-testing. Write test cases: inheritance FunctionsFrameworkExtensionRule, simulates the request and response objects, calls the function and asserts the response. Run the test: execute the mvn test command

How to automate integration testing of Java functions

Introduction

Automated integration testing is a crucial practice to verify that components work properly after integration, and the same is true for Java functions. This article will guide you on how to automate integration testing of Java functions using JUnit, Mockito, and Cloud Functions Framework.

Install dependencies

Add the following dependencies to your project:

<dependency>
  <groupId>junit</groupId>
  <artifactId>junit</artifactId>
  <version>4.13.2</version>
  <scope>test</scope>
</dependency>
<dependency>
  <groupId>org.mockito</groupId>
  <artifactId>mockito-core</artifactId>
  <version>4.6.1</version>
  <scope>test</scope>
</dependency>
<dependency>
  <groupId>com.google.cloud</groupId>
  <artifactId>google-cloud-functions-framework-testing</artifactId>
  <version>3.4.1</version>
  <scope>test</scope>
</dependency>

Write test cases

Create a test class, inherited from FunctionsFrameworkExtensionRule:

import static com.google.common.truth.Truth.assertThat;
import static org.mockito.Mockito.when;

import com.google.cloud.functions.HttpRequest;
import com.google.cloud.functions.HttpResponse;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.StringReader;
import java.nio.charset.StandardCharsets;
import java.util.Map;
import org.junit.Before;
import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.TestRule;
import org.mockito.Mock;
import org.mockito.MockitoAnnotations;

public class ExampleFunctionTest {

  @Rule
  public TestRule FUNCTIONS_FRAMEWORK_TEST_RULE = new FunctionsFrameworkExtensionRule();

  @Mock
  private HttpRequest request;

  @Mock
  private HttpResponse response;

  private BufferedWriter writerOut;
  private PrintWriter printWriter;

  @Before
  public void beforeEach() {
    MockitoAnnotations.initMocks(this);
    writerOut = new BufferedWriter(new PrintWriter(response.getWriter()));
    printWriter = new PrintWriter(writerOut, true);
  }

  @Test
  public void helloHttp_shouldPrintAName() throws IOException {

    // Mock request
    when(request.getReader()).thenReturn(new StringReader("{}"));

    // Invoke function under test
    new ExampleFunction().service(request, response);

    // Assert that the function writes "Hello World!" to the response
    writerOut.flush();
    assertThat(printWriter.toString()).isEqualTo("Hello World!");
  }
}

Practical case

In the above test case, we tested the ExampleFunction function , the function printed a message. The test simulates the request object and response object, calls the function and asserts that the expected message is present in the response.

Run the test

To run the test, run the mvn test command.

Conclusion

By using JUnit, Mockito, and Cloud Functions Framework, you can easily automate integration testing of Java functions. This helps ensure that your function still works properly after being integrated with other components.

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