Given below are some noteworthy JUnit concepts, as per the JUnit 5 User Guide.
Annotations: In addition to the
@Testannotation you've seen already, there are many other annotations in JUnit. For example, the@Disabledannotation can be used to disable a test temporarily. [more ...]Pre/post-test tasks: In order to allow individual test methods to be executed in isolation and to avoid unexpected side effects due to mutable test instance state, JUnit creates a new instance of each test class before executing each test method. It is possible to supply code that should be run before/after every test method/class (e.g., for setting up the environment required by the tests, or cleaning up things after a test is completed) by using test instance lifecycle annotations such as
@BeforeEach@AfterAll. [more ...]Conditional test execution: It is possible to configure tests to run only under certain conditions. For example,
@TestOnMacannotation can be used to specify tests that should run on Mac OS only. [more ...]Assumptions: It is possible to specify assumptions that must hold for a test to be executed (i.e., the test will be skipped if the assumption does not hold). [more ...]
Tagging tests: It is possible to tag tests (e.g.,
@Tag("slow")so that tests can be selected based on tags. [more ...]Test execution order: By default, JUnit executes test classes and methods in a deterministic but intentionally nonobvious order. This ensures that subsequent runs of a test suite execute tests in the same order, thereby allowing for repeatable builds. But it is possible to specify a specific testing order. [more ...]
Test hierarchies: Normally, we organize tests into separate test classes. If a more hierarchical structure is needed, the
@Nestedannotation can be used to express the relationship among groups of tests. [more ...]Repeated tests: JUnit provides the ability to repeat a test a specified number of times by annotating a method with
@RepeatedTestand specifying the total number of repetitions desired. [more ...]Parameterized tests make it possible to run a test multiple times with different arguments. The parameter values can be supplied using a variety of ways e.g., an array of values, enums, a csv file, etc. [more ...]
Dynamic tests: The
@TestFactoryannotation can be used to specify factory methods that generate tests dynamically. [more ...]Timeouts: The
@Timeoutannotation allows one to declare that a test should fail if its execution time exceeds a given duration. [more ...]Parallel execution: By default, JUnit tests are run sequentially in a single thread. Running tests in parallel — for example, to speed up execution — is available as an opt-in feature. [more ...]
Extensions: JUnit supports third-party extensions. The built-in
TempDirectoryextension is used to create and clean up a temporary directory for an individual test or all tests in a test class. [more ...]