Unit testing Android Apps

I have written about unit testing in other posts so this time I will only focus on how to create a test suite and test cases for Android applications. Writing unit tests for Java is a little different than doing it for other languages like JavaScript because Java is not only a strongly typed language, but also is a lot less dynamic than JavaScript.

Creating a test suite

Good developers create tests for all their projects, and for Android there is an standard place where those tests live. Although you don’t really have to do this, it is recommended that you create a tests/ folder in the root of the Android project under test, at the same level as the src/ folder:

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MyProject/
    AndroidManifest.xml
    src/
    ...
    tests/
        AndroidManifest.xml
        src/
        ...

Now that we know where we want our tests to live we can go ahead and create a test suite using the android tool:

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/path/to/android-sdk/tools/android create test-project \
-n MyProjectTests \
-p /path/to/MyProject/tests \
-m ../

This commands create a new test project in a tests/ folder inside of our application under test. This is how it works:

• -n A name for your test project. Usually the same name as the application under test + Tests at the end.
• -p Path to the folder where you want to create the test project. It is recommended to do it in a folder called tests inside your main app
• -m Path to the main application under test, relative to the test project. If you follow the convention of always placing your tests in a tests folder inside your main app, this will always be ../

After running this command we can make sure everything works fine by building our tests:

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cd /path/to/MyProject/tests
ant debug

After building the tests you will need to start an emulator and install your tests package on it before you can run them:

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/path/to/android-sdk/tools/emulator -avd EmulatorName &
cd /path/to/MyProject/tests
/path/to/android-sdk/platform-tools/adb -s emulator-5554 \
install /path/to/MyProject/tests/bin/MyProjectTests-debug.apk
ant test

And you should get an output similar to:

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test:
     [echo] Running tests ...
     [exec]
     [exec] Test results for InstrumentationTestRunner=
     [exec] Time: 0.001
     [exec]
     [exec] OK (0 tests)
     [exec]
     [exec]

BUILD SUCCESSFUL

So far we only created a test suite and ran it, we haven’t actually created any tests. If you have done unit testing in other programming languages you might have also noticed that doing it for Android requires a few more steps that can make it feel a little cumbersome. There are some options to make this process a little easier but I wont cover them in this post.

Writing tests

Lets start by modifying our generated test file and adding a simple assertion to it. If you look at /path/to/MyProject/tests/src/com/example/myproject/MyProjectTest.java you will find something like this:

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package com.example.myproject;

import android.test.ActivityInstrumentationTestCase2;

public class MyProjectTest extends ActivityInstrumentationTestCase2<MyProject> {

    public MyProjectTest() {
        super("com.example.myproject", MyProject.class);
    }

}

You can see that our MyProjectTest class extends from ActivityInstrumentationTestCase2, this means that this test file is intended to test an activity. Since I don’t want to go over all the types of tests that you can write for Android I will replace it with a generic test case and write a simple assertion:

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package com.example.myproject;

import android.test.AndroidTestCase;
import junit.framework.Assert;

public class MyProjectTest extends AndroidTestCase {
    public void testSomething() {
        Assert.assertTrue(false);
    }
}

Notice that we are extending AndroidTestCase to write a more generic test. We also import JUnit’s assertion library so we can use it in our tests. Another important thing to mention is that the name of my test function is testSomething. All tests must start with test for them to be run when the test suite is ran.

Since I am ussing Assert.assertTrue against false when we run this test using the steps I explained above we will get a different output:

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test:
     [echo] Running tests ...
     [exec]
     [exec] com.example.myproject.MyProjectTest:.
     [exec] Failure in testSomething:
     [exec] junit.framework.AssertionFailedError
     [exec]     at com.example.myproject.MyProjectTest.testSomething(MyProjectTest.java:8)
     [exec]     at java.lang.reflect.Method.invokeNative(Native Method)
     [exec]     at android.test.AndroidTestRunner.runTest(AndroidTestRunner.java:190)
     [exec]     at android.test.AndroidTestRunner.runTest(AndroidTestRunner.java:175)
     [exec]     at android.test.InstrumentationTestRunner.onStart(InstrumentationTestRunner.java:555)
     [exec]     at android.app.Instrumentation$InstrumentationThread.run(Instrumentation.java:1661)
     [exec]
     [exec] Test results for InstrumentationTestRunner=..F
     [exec] Time: 0.041
     [exec]
     [exec] FAILURES!!!
     [exec] Tests run: 2,  Failures: 1,  Errors: 0
     [exec]
     [exec]

BUILD SUCCESSFUL

From here writing tests for your classes is just a matter of importing them in your test files, executing the methods you want to test and asserting that they do what you expected.