android_robolectric_tests.md

JUnit Tests

JUnit tests are Java unit tests. These tests run locally on your workstation.

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Writing a JUnit test

When writing JUnit tests, you must decide whether you need to use Android code. If you want to use Android code you must write a Robolectric test.

JUnit tests (without Android)

Build these types of test using the robolectric_binary GN template.

If you don't need to use any Android code in your tests, you can write plain, old JUnit tests. Some more documentation about writing JUnit tests can be found here.

Example Code

package org.chromium.sample.test;

import static org.junit.Assert.assertTrue;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.BlockJUnit4ClassRunner;

@RunWith(BlockJUnit4ClassRunner.class)
public class MyJUnitTest {

    @Test
    public void exampleTest() {
        boolean shouldWriteMoreJUnitTests = true;
        assertTrue(shouldWriteMoreJUnitTests);
    }
}

Example within Chromium

See the junit_unit_tests test suite.

JUnit tests with Robolectric

Build these types of test using the robolectric_binary GN template.

Robolectric is a unit testing framework that lets you run tests with Android code on your workstation. It does this by providing a special version of the Android SDK jar that can run in your host JVM. Some more information about Robolectric can be found here.

One on the main benefits of using Robolectric framework are shadow classes. Robolectric comes with many prebuilt shadow classes and also lets you define your own. Whenever an object is instantiated within a Robolectric test, Robolectric looks for a corresponding shadow class (marked by @Implements(ClassBeingShadowed.class)). If found, any time a method is invoked on the object, the shadow class's implementation of the method is invoked first. This works even for static and final methods.

Useful Tips

• Use @RunWith(BaseRobolectricTestRunner.class) for all Chromium Robolectric tests.
• You can specify the Android SDK to run your test with with @Config(sdk = ??).

Currently, only SDK levels 18, 21, and 25 are supported in Chromium but more can be added on request.

Example Code

package org.chromium.sample.test;

import static org.junit.Assert.assertTrue;

import android.text.TextUtils;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.robolectric.annotation.Config;

import org.chromium.base.test.BaseRobolectricTestRunner;

// Be sure to specify to run tests with a RobolectricTestRunner. The
// default JUnit test runner won't load the Robolectric Android code properly.
// BaseRobolectricTestRunner will do some common initializations. If this is
// not desired, then RobolectricTestRunner could be used directly.
@RunWith(BaseRobolectricTestRunner.class)
// Can specify some Robolectric related configs here.
// More about configuring Robolectric at http://robolectric.org/configuring/.
// SDK will default to the latest we support in Chromium.
@Config(manifest = Config.NONE, sdk = 21)
public class MyRobolectricJUnitTest {

    @Test
    public void exampleTest() {
        String testString = "test";

        // Even though these tests runs on the host, Android classes are
        // available to use thanks to Robolectric.
        assertTrue(TextUtils.equals(testString, "test"));
    }
}

Example robolectric_binary build template.

robolectric_binary("my_robolectric_tests") {

    sources = [
        "java/src/foo/bar/MyJUnitTest.java"
    ]

    deps = [
        "//my/test:dependency",
    ]

    # Sets app's package name in Robolectric tests. You need to specify
    # this variable in order for Robolectric to be able to find your app's
    # resources.
    package_name = manifest_package
}

Example within Chromium

See the content_junit_tests test suite.

Running JUnit tests

After writing a test, you can run it by:

1. Adding the test file to a robolectric_binary GN target.
2. Rebuild.
3. GN will generate binary <out_dir>/bin/run_<suite name> which can be used to run your test.

For example, the following can be used to run chrome_junit_tests.

# Build the test suite after adding our new test.
ninja -C out/Debug chrome_junit_tests

# Run the test!
out/Debug/bin/run_chrome_junit_tests