Package com.google.common.truth

Class ExpectFailure

java.lang.Object

com.google.common.truth.ExpectFailure

All Implemented Interfaces:

TestRule

public final class ExpectFailure
extends Object

A utility for testing that assertions against a custom Subject fail when they should, plus a utility to assert about parts of the resulting failure messages.

Usage:

   AssertionError failure =
       expectFailure(whenTesting -> whenTesting.that(cancelButton).isVisible());
   assertThat(failure).factKeys().containsExactly("expected to be visible");

 ...

 private static AssertionError expectFailure(
     ExpectFailure.SimpleSubjectBuilderCallback<UiElementSubject, UiElement> assertionCallback) {
   return ExpectFailure.expectFailureAbout(uiElements(), assertionCallback);
 }
 

Or, if you can't use lambdas:

 @Rule public final ExpectFailure expectFailure = new ExpectFailure();

 ...

     expectFailure.whenTesting().about(uiElements()).that(cancelButton).isVisible();
     assertThat(failure).factKeys().containsExactly("expected to be visible");
 

ExpectFailure is similar to JUnit's assertThrows (JUnit 4, JUnit 5). We recommend it over assertThrows when you're testing a Truth subject because it also checks that the assertion you're testing uses the supplied FailureStrategy and calls FailureStrategy.fail(java.lang.AssertionError) only once.

Nested Class Summary

Nested Classes

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

Constructor Summary

Constructors

Constructor	Description
ExpectFailure()	Creates a new instance for use as a @Rule.

Method Summary

Modifier and Type	Method	Description
Statement	apply(Statement base, Description description)
static TruthFailureSubject	assertThat(@Nullable AssertionError actual)	Creates a subject for asserting about the given AssertionError, usually one produced by Truth.
static AssertionError	expectFailure(ExpectFailure.StandardSubjectBuilderCallback assertionCallback)	Static alternative that directly returns the triggered failure.
static <S extends Subject,A> AssertionError	expectFailureAbout(Subject.Factory<S,A> factory, ExpectFailure.SimpleSubjectBuilderCallback<S,A> assertionCallback)	Static alternative that directly returns the triggered failure.
AssertionError	getFailure()	Returns the captured failure, if one occurred.
StandardSubjectBuilder	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()

Creates a new instance for use as a @Rule. See the class documentation for details, and consider using the lambda version instead.

Method Detail

whenTesting

public StandardSubjectBuilder whenTesting()

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

An instance of ExpectFailure supports only one whenTesting call per test method. The static expectFailure(com.google.common.truth.ExpectFailure.StandardSubjectBuilderCallback) method, by contrast, does not have this limitation.

getFailure

public AssertionError getFailure()

Returns the captured failure, if one occurred.

expectFailure

@CanIgnoreReturnValue
public static AssertionError expectFailure(ExpectFailure.StandardSubjectBuilderCallback 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

@CanIgnoreReturnValue
public static <S extends Subject,A> AssertionError expectFailureAbout(Subject.Factory<S,A> factory,
                                                                            ExpectFailure.SimpleSubjectBuilderCallback<S,A> 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());

assertThat

public static TruthFailureSubject assertThat(@Nullable AssertionError actual)

Creates a subject for asserting about the given AssertionError, usually one produced by Truth.

apply

@GwtIncompatible("org.junit.rules.TestRule")
public Statement apply(Statement base,
                       Description description)

Specified by:

apply in interface TestRule