Package com.google.common.truth

Class Expect

  • All Implemented Interfaces:
    TestRule
    @GwtIncompatible("JUnit4")
public final class Expect
extends StandardSubjectBuilder
implements TestRule
    A TestRule that batches up all failures encountered during a test, and reports them all together at the end (similar to ErrorCollector). It is also useful for making assertions from other threads or from within callbacks whose exceptions would be swallowed or logged, rather than propagated out to fail the test. (AssertJ has a similar feature called "soft assertions"; however, soft assertions are not safe for concurrent use.)

    Usage: 

     @Rule public final Expect expect = Expect.create();

 ...

   expect.that(results).containsExactly(...);
   expect.that(errors).isEmpty();
    If both of the assertions above fail, the test will fail with an exception that contains information about both.

    Expect may be used concurrently from multiple threads. However, multithreaded tests still require care:

    • Expect has no way of knowing when all your other test threads are done. It simply checks for failures when the main thread finishes executing the test method. Thus, you must ensure that any background threads complete their assertions before then, or your test may ignore their results.
    • Assertion failures are not the only exceptions that may occur in other threads. For maximum safety, multithreaded tests should check for such exceptions regardless of whether they use Expect. (Typically, this means calling get() on any Future returned by a method like executor.submit(...). It might also include checking for unexpected log messages or reading metrics that count failures.) If your tests already check for exceptions from a thread, then that will cover any exception from plain assertThat.

    To record failures for the purpose of testing that an assertion fails when it should, see ExpectFailure.

    For more on this class, see the documentation page.