How to use googletest for testing C++ code that calls into java on android?

Testing C++ Code Calling Java on Android with GoogleTest

This article guides you through the process of using GoogleTest to write unit tests for C++ code that interacts with Java on the Android platform. This setup allows you to thoroughly test your C++ components, including those that rely on Java functionality.

Setting Up Your Development Environment

Before starting, ensure you have the following set up:

• Android Studio (with the necessary Android SDK components)
• CMake (for building your C++ code)
• GoogleTest (downloadable from GitHub or through your package manager)

Creating a Test Project

In Android Studio, create a new project:

• Choose “Empty Activity” as your project template.
• Set your project name and location.

Setting up GoogleTest

Follow these steps to integrate GoogleTest into your project:

1. Include GoogleTest in Your Project

• Download GoogleTest from https://github.com/google/googletest.
• Copy the “googletest” folder into your project’s “app/jni” directory.

2. Configure CMake for GoogleTest

• Edit the “app/CMakeLists.txt” file. Add the following lines within your CMakeLists.txt file:

add_subdirectory(googletest)

include_directories(${googletest_SOURCE_DIR}/include)

# ... Your other CMake configurations

3. Create Your Test File

• Create a new C++ source file in your “app/jni” directory (e.g., “my_test.cpp”).
• Include the GoogleTest header file:

#include "gtest/gtest.h"

Writing Your Test Cases

Now, you can write test cases that exercise your C++ code.

1. Define Test Fixtures

Create test fixtures for organizing your tests. This class defines common setup and teardown for related test cases.

class MyTest : public ::testing::Test {
protected:
    void SetUp() override {
        // Setup for your tests here
    }

    void TearDown() override {
        // Teardown for your tests here
    }
};

2. Write Individual Test Cases

Implement test cases within the test fixture. Each test case should verify specific functionality or behavior.

TEST_F(MyTest, TestFunction1) {
    // Call your C++ function
    // Assert expected results
    ASSERT_TRUE(result); 
}

TEST_F(MyTest, TestFunction2) {
    // Call your C++ function
    // Assert expected results
}

Interfacing with Java

To test C++ code calling into Java, you’ll use the Java Native Interface (JNI):

1. Create Your Java Class

• Create a Java class in your Android project’s “app/src/main/java” directory. This class will contain the Java functions you want to call from your C++ code.

package com.example.yourpackage;

public class MyJavaClass {
    public static native int nativeMethod(int value);

    static {
        System.loadLibrary("native-lib");
    }
}

2. Create Your C++ Wrapper

• Create a C++ header file (e.g., “jni_wrapper.h”) to define functions for calling into Java.

#include 
#include "com_example_yourpackage_MyJavaClass.h"

extern "C" JNIEXPORT jint JNICALL Java_com_example_yourpackage_MyJavaClass_nativeMethod(JNIEnv* env, jobject thiz, jint value) {
    // Your implementation here
    return value * 2;
}

3. Call Java Functions in Your Tests

• In your test cases, include the header file and use the wrapper functions to call Java methods.

TEST_F(MyTest, TestJavaCall) {
    int result = jni_wrapper::nativeMethod(10);
    ASSERT_EQ(20, result);
}

Running Tests

To run your tests, build your project in Android Studio. Once the build is complete, you will find the test results in the “app/build/reports/tests/debug” directory.

Comparison Table

Example Code

This example demonstrates the basic concepts:

// app/jni/my_test.cpp
#include "gtest/gtest.h"
#include "jni_wrapper.h"

class MyTest : public ::testing::Test {
};

TEST_F(MyTest, TestFunction1) {
    // Your test logic
}

TEST_F(MyTest, TestJavaCall) {
    int result = jni_wrapper::nativeMethod(10);
    ASSERT_EQ(20, result);
}

// app/src/main/java/com/example/yourpackage/MyJavaClass.java
package com.example.yourpackage;

public class MyJavaClass {
    public static native int nativeMethod(int value);

    static {
        System.loadLibrary("native-lib");
    }
}

// app/jni/jni_wrapper.h
#include 
#include "com_example_yourpackage_MyJavaClass.h"

extern "C" JNIEXPORT jint JNICALL Java_com_example_yourpackage_MyJavaClass_nativeMethod(JNIEnv* env, jobject thiz, jint value) {
    return value * 2;
}

Conclusion

GoogleTest provides a robust and flexible framework for testing C++ code, including scenarios where you call Java functions from your native code. This enables you to thoroughly validate the behavior of your C++ components within your Android application.