AssertJ User Guide

Assertions

All AssertJ assertions are static methods in the org.assertj.core.api.Assertions class.

AssertJ assertions always look like assertThat(testedValue).<condition>(realValue).

For example, when we want to check if objects are equal, we would use:

assertThat("actual string").isEqualTo("expected string")

If we would like to to add a description to our assertion, we would use as(description).

For example:

assertThat("actual string").as("Values should be equal").isEqualTo("expected string")

Assertion	Condition
fail()	Fails a test with the given failure message
isTrue()	If we want to verify that a boolean value is true
isSameAs(object)	If we want to ensure that two objects refer to the same object
isNull()	If we want to verify that an object is null
hasSize(int)	If we want to verify size of collection
isEmpty()	If we want to verify that collection is empty
isNotSameAs(object)	If we want to ensure that two objects don't refer to the same object
isNotEqualTo(object)	If we want to verify that the expected value (or object) is not equal to the actual value (or object)
isNotNull()	If we want to verify that an object is not null
isFalse()	If we want to verify that a boolean value is false
isEqualTo()	If we want to verify that the expected value (or object) is equal to the actual value (or object)
isThrownBy(supplier)	If we want to write assertions for the exceptions thrown by the system

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Last update: 2020-12-07