Android : Difference between testImplementation, implementation, testCompileOnly and api

 In the context of Android development and Gradle (the build system used for Android projects), the terms testImplementation, implementation, testCompileOnly, and api are related to dependency configurations. These configurations determine how dependencies are included in your project and which parts of your project have access to those dependencies. Let's break down each one:

1. implementation:

   • Dependencies declared with implementation are available to the main source set (the main body of your application code) and are internal to the module where they are declared.
   • These dependencies are not exposed to other modules that depend on the current module.

   Example:

   gradle
   implementation 'com.example:library:1.0.0'
   

2. testImplementation:

   • Dependencies declared with testImplementation are only available during the test compilation and execution phases.
   • They are not included in the main source set and won't be packaged with the final APK. These dependencies are meant for testing purposes.

   Example:

   gradle
   testImplementation 'junit:junit:4.13.2'
   

3. testCompileOnly:

   • Dependencies declared with testCompileOnly are similar to testImplementation in that they are used only during the test compilation and execution phases.
   • However, they are not included in the test runtime classpath.

   Example:

   gradle
   testCompileOnly 'com.example:test-utils:1.0.0'
   

4. api:

   • Dependencies declared with api are part of the public API of the library/module.
   • They are visible to and can be used by other modules that depend on the current module.

   Example:

   gradle
   api 'com.example:shared-library:1.0.0'
   

In summary:

• Use implementation for dependencies that are internal to your module.
• Use testImplementation for dependencies needed only during testing.
• Use testCompileOnly for dependencies that are needed during testing but not at runtime.
• Use api for dependencies that are part of the public API and should be accessible to other modules.

Understanding these configurations is crucial for managing dependencies efficiently and ensuring that your project's structure is well-defined and maintainable.