ExternalUberServiceTest class has a getPriceEstimateBaseUrlTest() method. This is a JUnit only unit test for the buildPriceEstimateBaseUrl() method and doesn’t involve Mockito. Run it and you’ll see it pass.

We’ll be writing unit tests for the getPriceEstimates() method. The getPriceEstimates() method should return an empty array if any of the input coordinates are invalid. The getPriceEstimatesWithoutMockTest() test checks for this case.

public void getPriceEstimatesWithoutMockTest() {

    // Setup

    Double startLatitude = 137.775231;

    Double startLongitude = -122.418075;

    Double endLatitude = 37.775241;

    Double endLongitude = -122.518075;

    

    ExternalUberService externalUberService = new ExternalUberService();


    // Get output of the method under test

    PriceEstimate[] actualPriceEstimates = externalUberService.getPriceEstimates(

      startLatitude, startLongitude, endLatitude, endLongitude);


    // Check if the returned value matches expected value

    int expectedLength = 0;

    assertEquals(expectedLength, actualPriceEstimates.length);

  }

TODO -

• Run getPriceEstimatesWithoutMockTest(). Does the test pass?

• Check the error response. Why do you think the test is failing?

You’d have found that the test failed.

The test report is mentioning that the googleMapsHelper field is null. You’d recall isValidLocations() is an abstract method in the GoogleMapsHelper interface. (Comment out getPriceEstimatesWithoutMockTest(), we’ll write a different test that works)

To test getPriceEstimates(), we’ll mock GoogleMapsHelper and set the googleMapsHelper field of the ExternalUberService instance as this mock object in the test. This allows you to pre-set an output which is returned when isValidLocations() is called with a specific input from the test. By mocking, we’re basically removing the dependency of the Code Under Test (getPriceEstimates()) on isValidLocations()

The getPriceEstimatesReturnsEmptyArrayOnInvalidStartLatitudeTest() test checks if the getPriceEstimates() method returns an empty array when the starting location latitude is invalid. You can see the valid range of latitude is from -90 to +90 in the GoogleMapsHelper contract. The starting location latitude given in the test doesn’t fall in this interval.

Below is the test code

// 1

@Mock

private GoogleMapsHelper googleMapsHelperMock;


public void getPriceEstimatesReturnsEmptyArrayOnInvalidStartLatitudeTest() {

    // 2. Setup

    Double startLatitude = 137.775231;

    Double startLongitude = -122.418075;

    Double endLatitude = 37.775241;

    Double endLongitude = -122.518075;

    

    // 3. 

    ExternalUberService externalUberService = new ExternalUberService();

    externalUberService.setGoogleMapsHelper(googleMapsHelperMock);


    // 4. Setup mock to return preset value of false

    // when startLatitude parameter is 137.775231

    when(googleMapsHelperMock.isValidLocations(eq(137.775231), anyDouble(), anyDouble(), anyDouble()))

      .thenReturn(false);


    // 5. Get output of the method under test

    PriceEstimate[] actualPriceEstimates = externalUberService.getPriceEstimates(

      startLatitude, startLongitude, endLatitude, endLongitude);


    // 6. Check if the returned value matches expected value

    int expectedLength = 0;

    assertEquals(expectedLength, actualPriceEstimates.length);

  }

1. The @Mock annotation is used to create a Mock object of type GoogleMapsHelper, googleMapsHelperMock (this is done at the class level)

2. The input coordinate values are initialized

3. Created an ExternalUberService object and set its googleMapsHelper field value to googleMapsHelperMock

4. Use Mockito when().thenReturn() statement to return false when the isValidLocations() method of the googleMapsHelperMock object is called with the the startLatitude value of 137.775231 and any Double value for other parameters. eq() and anyDouble() are Mockito argument matchers. anyDouble() matches with any Double value while eq() requires the exact value inside it to get matched.

5. The function to test is called

6. Validate if the output is as expected

We’ve created the Mock object for googleMapsHelper and set it to return false when called with the correct arguments. The test should pass now, right? Try running it.

It’s still failing!

To allow the JUnit test class to support Mocks, we need to register the Mockito extension for the test class. @ExtendWith(MockitoExtension.class) annotation does this.

@ExtendWith(MockitoExtension.class)

public class ExternalUberServiceTest {

The test will pass now.

Confused which object(s) to Mock and what to return? Use this framework to your aid

Code Under Test: ExternalUberService.getPriceEstimates()

Test case: Check if ExternalUberService.getPriceEstimates() returns empty

array on invalid latitude for start location

Dependency Layer/Function:

  1. googleMapsHelper.isValidLocation(String startLatitude, String startLongitude,

    String endLatitude, String endLongitude);

Mock Setup:

  - Function to mock: googleMapsHelper.isValidLocation()

    - Input to mock: (some invalid start latitude, any start longitude, any end

        latitude, any end longitude)

    - Pre-set output from mock: false

Test Input: externalUberService.getPriceEstimates()(parameters should be

inline with your mock setup)

Expected Test Output: Empty price estimate array

Feel free to add more tests to check if getPriceEstimates() return an empty array when the other coordinates (startLongitude, endLatitude, endLongitude) are invalid