Learn Java Unit Testing with Junit & Mockito in 30 Steps

Discover why unit testing matters by validating a single method in isolation with automated checks. See how unit tests run in milliseconds to verify outputs and catch defects.

Set up your first JUnit test by creating a new Maven project in Eclipse, organizing code in src/main/java and tests in src/test/java, and adding JUnit 4 to the build path.

Transform a failing JUnit test into a passing one by using assertEquals to compare expected and actual values, and practice testing with StringHelper's truncateAinFirst2Positions to produce a green bar.

Refactor and rename the first JUnit test to clearly indicate the tested method, split conditions into separate public void tests, and reduce duplication with a class-level instance and assertEquals.

Explore second jUnit example by testing areFirstAndLastTwoCharactersTheSame with @Test, assertEquals, assertFalse, and assertTrue, including scenarios for ABCD, ABAB, AB, and single-character inputs, plus test naming and running tests.

Ranga Karanam, founder of in28Minutes and the course's primary instructor, shares two decades of programming in Java, Python, and JavaScript, and highlights cloud certifications and a passion for simplifying technology.

Learn how @Before and @After run before and after every test method to handle setup and teardown, creating fresh test data and cleaning up after tests.

Discover how @BeforeClass and @AfterClass run once per test class, initialize static resources, and optimize performance by avoiding per-test setup and teardown.

Learn how to compare arrays in JUnit tests with Arrays.sort (in-place ascending) and assertArrayEquals to verify values, and read clear failure messages.

Learn how to test exceptions in JUnit by triggering a null pointer exception with Arrays.sort on a null array, and declaring expected exceptions with @Test(expected=...).

Assess sorting performance of millions of 3-element arrays in JUnit tests by benchmarking within a strict timeout, accounting for build server variability.

Explore parameterized tests in junit, using @RunWith(Parameterized.class) and @Parameters to define input-output pairs, wire them through a constructor, and run multiple test conditions from a collection.

Organize Java unit tests into suites to run selective groups. Create a JUnit test suite, include multiple test classes with @SuiteClasses, and execute only the chosen tests.

Remember things for a long time by practicing active learning and taking notes, then reviewing those notes regularly to reinforce programming concepts and frameworks.

Troubleshoot on your own to build resilience, then search Google and use ChatGPT with questions, caution about data, post queries in Q&A, and help others; take a break if needed.

Explore core Java unit testing with JUnit and Mockito, covering basics, exceptions, and performance, plus Mockito advanced features, annotations and runners, and Powermock integration for static methods and constructors.

Set up a Maven-based Java project in eclipse with junit and Mockito, configure dependencies via pom.xml, and run a first unit test to validate the environment.

Explore unit testing with Mockito by defining the system under test, creating a to-do service and a to-do business implementation, and using stubs to drive tests.

Set up the system under test with TodoBusinessImpl and TodoService, then filter spring-related todos to illustrate mocks and stubs for unit testing.

test the todo business impl using a todo service stub to return dummy data and verify the results. highlight the disadvantages of stubbing, including maintenance headaches and limited dynamic scenarios.

Master Mockito by creating mocks and replacing stubs with when-then-return in a TodoService test. Learn to configure static imports, IDE hints, and basic mock behavior in JUnit workflows.

Build a consistent study habit by dedicating a few hours daily to improve long-term retention, and create a two-week plan with lecture ranges visible for accountability.

Master the basics of Mockito by mocking the list interface, returning different values on subsequent calls, using argument matches, throwing exceptions, writing BDD-style tests, and verifying method calls.

Learn how to mock the java.util List with Mockito, stub methods to return multiple values, use argument matchers like anyInt, and throw exceptions in tests.

Learn how to write unit tests with BDD style using Mockito and BDDMockito, applying given-when-then, given willReturn, and assertThat with hamcrest for readable tests.

Master verifying mock interactions in JUnit and Mockito by testing that specific methods are called. Verify not called, or called a precise number of times, using verify and related patterns.

Learn how to capture arguments passed to a mock in Mockito using argument captor, compare single and multiple invocations, and switch from verify to then for BDD style.

Teaching others deepens understanding, enhances communication, and builds confidence by simplifying complex ideas. Encourage learning, expand knowledge, and foster empathy by considering the learner's perspective.

Add the hamcrest library to your pom and write readable assertions with Hamcrest matchers for lists, arrays, and empty or null strings, including size and items checks.

Master Mockito annotations such as @Mock, @InjectMocks, @RunWith, and @Captor to auto-wire dependencies, reduce boilerplate, and improve test readability with argument captors.

Discover how JUnit rules replace runners, wiring mocks and dependencies with MockitoRule and @Rule for flexible, multiple-test setup.

Learn how to write real-world unit tests with Mockito and Spring by mocking dependencies in a multi-layered Java project, including tests for getClientProductsSum, saveChangedProducts, and calculateAndSaveClientProductSum.

Learn how to use mocks and spies in Mockito: wrap a real object, override specific methods, verify calls, and decide when to use a spy for legacy code.

Explore why Mockito forbids stubbing final or private methods and promotes testing via public interfaces, and note limitations on final and static method mocks.

Practice deep work by maintaining a distraction-free environment and scheduling two to three hour blocks weekly to achieve flow, maximize efficiency, and learn complex concepts quickly.

Set up PowerMock with Mockito to mock a static method, add powermock-api-mockito and powermock-module-junit4 dependencies, and write a unit test for SystemUnderTest using the PowerMock runner and verifyStatic.

Learn to mock a static method in Java unit tests using PowerMockito and Mockito. Configure PowerMockRunner, PrepareForTest, and mockStatic, then verifyStatic to ensure the static method is invoked.

Learn to invoke a private method using PowerMock and Mockito with Whitebox, testing a private method in a legacy system while mocking dependencies and static calls.

Learn to mock a constructor using PowerMockito and Mockito by overriding ArrayList creation and returning a mock list with a controlled size in the system under test.

Improve unit test readability and ensure tests fail only on real logic issues by naming tests clearly, using given-when-then, and employing mocks to isolate external dependencies with Mockito.