TestRule (JUnit API)
Date: 2011-08-22

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## org.junit.rules
Interface TestRule

All Known Implementing Classes:
  ErrorCollector, ExpectedException, ExternalResource, TemporaryFolder, TestName, TestWatcher, Timeout, Verifier

    public interface TestRule

A TestRule is an alteration in how a test method, or set of test methods, is run and reported. A `TestRule` may add additional checks that cause a test that would otherwise fail to pass, or it may perform necessary setup or cleanup for tests, or it may observe test execution to report it elsewhere. `TestRule`s can do everything that could be done previously with methods annotated with `Before`, `After`, `BeforeClass`, or `AfterClass`, but they are more powerful, and more easily shared between projects and classes. The default JUnit test runners for suites and individual test cases recognize `TestRule`s introduced in two different ways. `Rule` annotates method-level `TestRule`s, and `ClassRule` annotates class-level `TestRule`s. See Javadoc for those annotations for more information. Multiple `TestRule`s can be applied to a test or suite execution. The `Statement` that executes the method or suite is passed to each annotated `Rule` in turn, and each may return a substitute or modified `Statement`, which is passed to the next `Rule`, if any. For examples of how this can be useful, see these provided TestRules, or write your own:

- `ErrorCollector`: collect multiple errors in one test method
- `ExpectedException`: make flexible assertions about thrown exceptions
- `ExternalResource`: start and stop a server, for example
- `TemporaryFolder`: create fresh files, and delete after test
- `TestName`: remember the test name for use during the method
- `TestWatcher`: add logic at events during method execution
- `Timeout`: cause test to fail after a set time
- `Verifier`: fail test if object state ends up incorrect

Method Summary
`Statement` | `apply(Statement base, Description description)` Modifies the method-running `Statement` to implement this test-running rule.

Method Detail

### apply

    Statement apply(Statement base,
                    Description description)

  Modifies the method-running `Statement` to implement this test-running rule.

  Parameters:
    `base` - The `Statement` to be modified
    `description` - A `Description` of the test implemented in `base`
  Returns:
    a new statement, which may be the same as `base`, a wrapper around `base`, or a completely new Statement.

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