com.google.common.truth

Class ExpectFailure

java.lang.Object

com.google.common.truth.ExpectFailure

All Implemented Interfaces:

org.junit.rules.TestRule

public final class ExpectFailure
extends Object
implements org.junit.rules.TestRule

An assertion strategy that expects the given assertion to fail, and captures the failure rather than throwing it. It should be used as a JUnit @Rule, so that unexpectedly-passing assertions will cause your test to fail. In Java 8 you can use expectFailure() to instead capture failures directly.

By design this class expects exactly one failure per instance, meaning you should create separate tests for each failure case you intend to assert on, rather than trying to capture multiple failures in a single test. With expectFailure() you can safely capture multiple failures in the same test method, but creating separate tests is still encouraged. (Currently, calling whenTesting() more than once on the same instance fails. However, you should not rely on this behaviour.)

Note: this class is not intended for general use; it exists primarily to write tests of Subject implementations and other Truth internals. If you are writing your own custom subject you are encouraged to use this class rather than define a custom FailureStrategy or directly catch AssertionError. Use expectFailure.whenTesting().about(subjectFactory()).that(...) to make assertions about custom subjects.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	ExpectFailure.AssertionCallback A "functional interface" for expectFailure() to invoke and capture failures.
static interface	ExpectFailure.DelegatedAssertionCallback<S extends Subject<S,D>,D> A "functional interface" for expectFailureAbout() to invoke and capture failures.

Constructor Summary

Constructors

Constructor and Description
ExpectFailure()

Method Summary

Modifier and Type	Method and Description
org.junit.runners.model.Statement	apply(org.junit.runners.model.Statement base, org.junit.runner.Description description)
static AssertionError	expectFailure(ExpectFailure.AssertionCallback assertionCallback) Static alternative that directly returns the triggered failure.
static <S extends Subject<S,D>,D> AssertionError	expectFailureAbout(SubjectFactory<S,D> factory, ExpectFailure.DelegatedAssertionCallback<S,D> assertionCallback) Static alternative that directly returns the triggered failure.
AssertionError	getFailure() Returns the captured failure, if one occurred.
TestVerb	whenTesting() Returns a test verb that expects the chained assertion to fail, and makes the failure available via getFailure().

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ExpectFailure

public ExpectFailure()

Method Detail

whenTesting

public TestVerb whenTesting()

Returns a test verb that expects the chained assertion to fail, and makes the failure available via getFailure().

getFailure

public AssertionError getFailure()

Returns the captured failure, if one occurred.

expectFailure

public static AssertionError expectFailure(ExpectFailure.AssertionCallback assertionCallback)

Static alternative that directly returns the triggered failure. This is intended to be used in Java 8 tests similar to expectThrows():

AssertionError failure = expectFailure(whenTesting -> whenTesting.that(4).isNotEqualTo(4));

expectFailureAbout

public static <S extends Subject<S,D>,D> AssertionError expectFailureAbout(SubjectFactory<S,D> factory,
                                                                           ExpectFailure.DelegatedAssertionCallback<S,D> assertionCallback)

Static alternative that directly returns the triggered failure. This is intended to be used in Java 8 tests similar to expectThrows():

AssertionError failure = expectFailureAbout(myTypes(), whenTesting -> whenTesting.that(myType).hasProperty());

apply

public org.junit.runners.model.Statement apply(org.junit.runners.model.Statement base,
                                               org.junit.runner.Description description)

Specified by:

apply in interface org.junit.rules.TestRule