Android Unit Testing

Before Android Studio incorporated JUnit4, Google’s implementation was an odd mix of standard and Android specific unit tests.   The current version of JUnit4 is a much more vanilla implementation of the JUnit standard, see for more information or for the source code. The current recommended version of JUnit we’re loading in the build.gradle file is 4.12.

1. Android Assertions

In our Hello, World example we used the assertEquals assertion, but there are other assertions we can use in JUnit 4.12.

Android Assertions

There are also many other asserts that you can use if you add Hamcrest, assertj or any of the many other assert libraries.  But for the moment let’s start with the basic JUnit assertions.

assertTrue and assertFalse, when you’re looking for a true from a boolean condition and a false, for example assertTrue (5 < 6) and assertFalse (5>6)

assertNull and assertNotNull checks to see if an object is null e.g. assertNull(Calculator) or assertNotNull(Calculator) 

assertSame and assertNotSame checks the two objects are references to the same object for assertSame or not for assertNotSame. This is not the same as equals which compares the values of the two objects and not the object itself.

assertThat can be used like assertEquals where instead of saying we could now say
assertEquals(mCalculator.add(3, 4),7,0) we can say assertThat(mCalculator.add(3, 4), is(7))
fail is simply a failing test, for code that never should have been reached or to tell you here be dragons.

2. Command Line

Unit tests can be run from the command line using the following command

gradlew test --continue

The test task runs the unit tests and continue tells gradlew not to stop if any of the unit tests fail.

C:\Users\godfrey\AndroidStudioProjects\BasicSample>gradlew test --continue
Unzipping C:\Users\godfrey\.gradle\wrapper\dists\gradle-2.2.1-all\6dibv5rcnnqlfb
q9klf8imrndn\ to C:\Users\godfrey\.gradle\wrapper\dists\grad
:app:preBuild UP-TO-DATE
:app:preDebugBuild UP-TO-DATE


Total time: 3 mins 57.013 secs

First time you run a unit test you may run it from the command line using the gradlew test --continue command so that you can see what’s happening, or alternatively open the gradle console in Android Studio. Otherwise you may end up wondering why nothing is happening as Android Studio downloads all the necessary files to run unit tests.  

Command line execution of the tests is also very useful if you’re using a continuous integration build tool such as Jenkins.

3. jUnit Options

jUnit4 has the following annotations

  • @Before
  • @After
  • @Test
  • @BeforeClass
  • @AfterClass
  • @Test(timeout=ms)

@Test is used to annotate any test method, see Listing 1. @Test(timeout=ms) is a slight wrinkle on the standard annotation, it simply says give up if the test is taking longer than the defined timeout given in milliseconds.


public void calculator_CorrectSub_ReturnsTrue() {
  assertEquals(mCalculator.sub(4, 3),1,0);


Listing 1: @Test method

Before and After are used for any setup and teardown functions that you’re going to need. for example Before could include code to write to log files or creating objects to be used in the test or perhaps opening the database and then seeding the database with test data. After is typically used to reverse any of those Before changes, such as deleting the test rows in the database etc. see Listing 2.

public class CalculatorTest {


  private Calculator mCalculator;


  public void setUp() {

    mCalculator = new Calculator();



  public void calculator_CorrectAdd_ReturnsTrue() {
    assertEquals(mCalculator.add(3, 4),7,0);



  public void calculator_CorrectSub_ReturnsTrue() {
    assertEquals(mCalculator.sub(4, 3),1,0);



  public void calculator_CorrectMul_ReturnsTrue() {
    assertEquals(mCalculator.mul(3, 4),12,0);



  public void calculator_CorrectDiv_ReturnsTrue() {
    assertEquals(mCalculator.div(12, 4),3,0);


  public void tearDown() {
    mCalculator = null;

Listing 2: @Before and @After annotations

Before and After are called before every test, but if you want to make the setup changes only once before all the tests and once after all the tests then you should use @BeforeClass and @AfterClass. Note that setUp and tearDown methods now have to be declared as public static. The Calculator also has to be defined as static, see Listing 3 as there is now only one instance of the Calculator instead of one for each test.

private static Calculator mCalculator;


public static void setUp() {
  mCalculator = new Calculator();

Listing 3: Using BeforeClass instead of Before

4. HTML Output

JUnit outputs HTML and XML style reports in the \app\build\test-results\debug directory
These reports are useful mainly for reference when you’re trying to track exactly when a class or classes started to go fail or if some package or class has a higher tendency to fail than others, see figure 1.

HTML Reporting

Figure 1: HTML reporting

5. Grouping Tests

As your unit tests grow it’s not a bad idea to group them as small, medium or large tests based on how long they’re going to take.  Writing and executing unit tests should be lightning fast when you’re coding, but there may be more comprehensive tests that you might want to run once a day or when the code is checked in.

Figure 2 is taken from an old Google testing blog, see, which does a good job of showing when you should be grouping your tests into Medium or Large tests so they don’t slow down the development process.

Grouping Tests

Figure 2: Grouping Unit tests into categories

Small tests would be normal method based unit tests with mocked out database or network access.  Because Espresso tests need an emulator or device to run they would automatically be considered Medium or Large tests.

Listing 4, shows the normal way you would annotate whether a test is a small or medium test.


public void calculator_CorrectAdd_ReturnsTrue() {
  assertEquals(mCalculator.add(3, 4),7,0);



public void calculator_CorrectSub_ReturnsTrue() {
  assertEquals(mCalculator.sub(4, 3),1,0);



public void calculator_CorrectMul_ReturnsTrue() {
  assertEquals(mCalculator.mul(3, 4),12,0);



public void calculator_CorrectDiv_ReturnsTrue() {
  assertEquals(mCalculator.div(12, 4),3,0);


Listing 4: Classic Unit Testing Grouping

Unfortunately unit testing support isn’t perfect yet in Android Studio and there’s no way to tell Studio to only execute the small or medium suite of tests in the build.gradle file.  Until that changes for the moment the best workaround is to put the size in the test method name, see Listing 5. Gradle will let you use * to help define what tests you want to run. We can run only the small tests from the command line using the command gradlew testDebug --tests *Small* or for the medium size tests use gradlew testDebug --tests *Medium*.


public void calculator_CorrectSub__Small_ReturnsTrue() {
  assertEquals(mCalculator.sub(4, 3),1,0);



public void calculator_CorrectMul_Medium_ReturnsTrue() {
  assertEquals(mCalculator.mul(3, 4),12,0);


Listing 5: Grouping Tests

The XML output from the initial gradlew command is shown in Listing 6, which shows only the small tests ran.

<?xml version="1.0" encoding="UTF-8"?>
<testsuite name="com.riis.calculatordiv.CalculatorTest" tests="2" skipped="0" failures="0" errors="0" timestamp="2015-08-19T17:29:10" hostname="RIIS-Aspire-02" time="0.005">
  <testcase name="calculator_CorrectAdd__Small_ReturnsTrue" classname="com.riis.calculatordiv.CalculatorTest" time="0.003"/>
  <testcase name="calculator_CorrectSub__Small_ReturnsTrue" classname="com.riis.calculatordiv.CalculatorTest" time="0.001"/>
Listing 6: XML output showing for small test run.

6. Parameterized Tests

If we want to test our calculator we’re going to have to do a lot more testing than adding, subtracting, multiplying and dividing combinations of the numbers 3 and 4. Listing 7 has a few more tests to give us a little more confidence on our implementation. Run the tests and they should all pass.


public void calculator_CorrectAdd_ReturnsTrue() {
  assertEquals(mCalculator.add(3, 4),7,0);
  assertEquals(mCalculator.add(4, 3),7,0);
  assertEquals(mCalculator.add(8, 2),10,0);
  assertEquals(mCalculator.add(-1, 4),3,0);
  assertEquals(mCalculator.add(3256, 4),3260,0);

Listing 7: Adding more test conditions

If you’re writing unit tests, my guess is you are always looking for ways to write better code and the code Listing 7 smells. All that hard coding doesn’t look right, even if it’s test code.  We can use jUnit’s parameterized tests to tidy this up. 

Refactor your code to add parameterized tests as follows

  • Add @RunWith(Parameterized.class) at the top of the class to tell the compiler that we are using parameters for our testing

  • Add the import statement, import static org.junit.runners.Parameterized.Parameters;

  • Create your collections of tests parameters, in this case operandOne, operandTwo and the expectedResult

  • Add the constructor for the class

  • Use the parameters to feed your tests

The complete code is shown in Listing 8.  We’ve converted the code to work only with integers for simplicity sake

import org.junit.Before;

import org.junit.Test;

import org.junit.runner.RunWith;

import org.junit.runners.Parameterized;

import java.util.Arrays;

import java.util.Collection;

import static org.junit.Assert.assertEquals;

import static org.junit.runners.Parameterized.Parameters;


public class CalculatorParamTest {

  private int mOperandOne;
  private int mOperandTwo;
  private int mExpectedResult;


  private Calculator mCalculator;

  /* Array of tests */

  public static Collection<Object[]&gt> data() {
    return Arrays.asList(new Object[][] {
      {3, 4, 7},
      {4, 3, 7},
      {8, 2, 10},
      {-1, 4, 3},
      {3256, 4, 3260}

  /* Constructor */
  public CalculatorParamTest(int mOperandOne, int mOperandTwo, int mExpectedResult) {
    this.mOperandOne = mOperandOne;
    this.mOperandTwo = mOperandTwo;
    this.mExpectedResult = mExpectedResult;


  public void setUp() {
    mCalculator = new Calculator();


  public void testAdd_TwoNumbers() {
    int resultAdd = mCalculator.add(mOperandOne, mOperandTwo);
    assertEquals(resultAdd, mExpectedResult,0);


When the code runs we get the following results in the statistics frame, see figure 3.

Test Results

Figure 3: Parameterized test results.

Note a complete set of these testing blogs have been compiled together into an Agile Android mini-book, published by Apress and available from Amazon

This is Part 2 of 6, the remaining blogs can be found below.

Part 1 - Android Testing
Part 2 - Android Unit Testing
Part 3 - Hamcrest, JaCoCo, Mockito, and Jenkins for Android
Part 4 - Espresso Testing on Android
Part 5 - Android Mocking
Part 6 - Maintaining Someone Else’s Android Code