Unit Testing a Method: The Ultimate Guide to Map Lookup Testing

Preparing for the Unit Test

Before we start writing our unit test, let’s create a simple map lookup method that we can test. Here’s an example in Java:

public class PhoneNumberLookup {
  private Map<String, String> phonebook = new HashMap<>();

  public PhoneNumberLookup() {
    phonebook.put("John Doe", "123-456-7890");
    phonebook.put("Jane Doe", "098-765-4321");
  }

  public String lookupPhoneNumber(String name) {
    return phonebook.get(name);
  }
}

This method is straightforward – it creates a phonebook map and provides a lookupPhoneNumber method that takes a name as input and returns the corresponding phone number.

Writing the Unit Test

Now that we have our map lookup method, let’s write a unit test to ensure it’s working correctly. We’ll use JUnit as our testing framework.

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

public class PhoneNumberLookupTest {
  private PhoneNumberLookup phonebook = new PhoneNumberLookup();

  @Test
  public void testLookupPhoneNumber_HappyPath() {
    String phoneNumber = phonebook.lookupPhoneNumber("John Doe");
    assertEquals("123-456-7890", phoneNumber);
  }

  @Test
  public void testLookupPhoneNumber_KeyNotFound() {
    String phoneNumber = phonebook.lookupPhoneNumber("Unknown");
    assertNull(phoneNumber);
  }

  @Test
  public void testLookupPhoneNumber_NullKey() {
    assertThrows(NullPointerException.class, () -> phonebook.lookupPhoneNumber(null));
  }
}

Here, we’ve written three unit tests:

1. testLookupPhoneNumber_HappyPath: This test ensures that the method returns the correct phone number for a given name.
2. testLookupPhoneNumber_KeyNotFound: This test checks that the method returns null when the key is not found in the map.
3. testLookupPhoneNumber_NullKey: This test ensures that the method throws a NullPointerException when the input key is null.

Running the Unit Test

Now that we have our unit test, let’s run it to see if our map lookup method passes with flying colors! If you’re using an IDE like Eclipse or IntelliJ, you can simply right-click on the test class and select “Run.” If you’re running from the command line, you can use the following command:

java -jar junit-platform-console-standalone.jar -cp . PhoneNumberLookupTest

Assuming your test passes, you should see a message indicating that all tests were successful.

Best Practices for Unit Testing Map Lookups

Now that we’ve written and run our unit test, let’s discuss some best practices to keep in mind when testing map lookups:

• Test for happy paths**: Ensure that your method returns the correct value for a given key.
• Test for edge cases**: Check that your method handles null or empty keys, as well as keys that don’t exist in the map.
• Use a variety of test data**: Use different types of keys and values to ensure that your method is robust.
• Keep your tests independent**: Ensure that each test is independent of the others, so that a failure in one test doesn’t affect the others.