If your unit test has no dependencies or only has simple dependencies on Android, you should run your test on a local development machine. This testing approach is efficient because it helps you avoid the overhead of loading the target app and unit test code onto a physical device or emulator every time your test is run. Consequently, the execution time for running your unit test is greatly reduced. With this approach, you normally use a mocking framework, like Mockito, to fulfill any dependency relationships.
In your Android Studio project, you must store the source files for local
unit tests at module-name/src/test/java/. This directory
already exists when you create a new project.
You also need to configure the testing dependencies for your project to use the standard APIs provided by the JUnit 4 framework. If your test needs to interact with Android dependencies, include the Mockito library to simplify your local unit tests. To learn more about using mock objects in your local unit tests, see Mocking Android dependencies.
In your app's top-level {@code build.gradle} file, you need to specify these libraries as dependencies:
dependencies {
// Required -- JUnit 4 framework
testCompile 'junit:junit:4.12'
// Optional -- Mockito framework
testCompile 'org.mockito:mockito-core:1.10.19'
}
Your local unit test class should be written as a JUnit 4 test class. JUnit is the most popular and widely-used unit testing framework for Java. The latest version of this framework, JUnit 4, allows you to write tests in a cleaner and more flexible way than its predecessor versions. Unlike the previous approach to Android unit testing based on JUnit 3, with JUnit 4, you do not need to extend the {@code junit.framework.TestCase} class. You also do not need to prefix your test method name with the {@code ‘test’} keyword, or use any classes in the {@code junit.framework} or {@code junit.extensions} package.
To create a basic JUnit 4 test class, create a Java class that contains one or more test methods. A test method begins with the {@code @Test} annotation and contains the code to exercise and verify a single functionality in the component that you want to test.
The following example shows how you might implement a local unit test class. The test method {@code emailValidator_CorrectEmailSimple_ReturnsTrue} verifies that the {@code isValidEmail()} method in the app under test returns the correct result.
import org.junit.Test;
import java.util.regex.Pattern;
import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;
public class EmailValidatorTest {
@Test
public void emailValidator_CorrectEmailSimple_ReturnsTrue() {
assertThat(EmailValidator.isValidEmail("name@email.com"), is(true));
}
...
}
To test that components in your app return the expected results, use the junit.Assert methods to perform validation checks (or assertions) to compare the state of the component under test against some expected value. To make tests more readable, you can use Hamcrest matchers (such as the {@code is()} and {@code equalTo()} methods) to match the returned result against the expected result.
By default, the Android Plug-in for Gradle executes your local unit tests against a modified version of the {@code android.jar} library, which does not contain any actual code. Instead, method calls to Android classes from your unit test throw an exception.
You can use a mocking framework to stub out external dependencies in your code, to easily test that your component interacts with a dependency in an expected way. By substituting Android dependencies with mock objects, you can isolate your unit test from the rest of the Android system while verifying that the correct methods in those dependencies are called. The Mockito mocking framework for Java (version 1.9.5 and higher) offers compatibility with Android unit testing. With Mockito, you can configure mock objects to return some specific value when invoked.
To add a mock object to your local unit test using this framework, follow this programming model:
The following example shows how you might create a unit test that uses a mock {@link android.content.Context} object.
import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.CoreMatchers.*;
import static org.mockito.Mockito.*;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.Mock;
import org.mockito.runners.MockitoJUnitRunner;
import android.content.SharedPreferences;
@RunWith(MockitoJUnitRunner.class)
public class UnitTestSample {
private static final String FAKE_STRING = "HELLO WORLD";
@Mock
Context mMockContext;
@Test
public void readStringFromContext_LocalizedString() {
// Given a mocked Context injected into the object under test...
when(mMockContext.getString(R.string.hello_word))
.thenReturn(FAKE_STRING);
ClassUnderTest myObjectUnderTest = new ClassUnderTest(mMockContext);
// ...when the string is returned from the object under test...
String result = myObjectUnderTest.getHelloWorldString();
// ...then the result should be the expected one.
assertThat(result, is(FAKE_STRING));
}
}
To learn more about using the Mockito framework, see the Mockito API reference and the {@code SharedPreferencesHelperTest} class in the sample code.
To run your local unit tests, follow these steps:
in the toolbar.
..
.
The Android Plugin for Gradle compiles the local unit test code located in the default directory ({@code src/test/java/}), builds a test app, and executes it locally using the default test runner class. Android Studio then displays the results in the Run window.