AssertJ is an open source Java library for writing fluent assertions in your test code. It\u2019s an alternative to built-in assertions from the Junit testing framework or matchers from the Hamcrest library. It can help you write assertions that are more readable and closer to natural language. AssertJ API is also designed to be easily discoverable through IDE code completion.<\/p>\n\n\n\n
The most commonly used test assertions in Java are the ones from the Junit library, like assertEquals. The order of parameters in these assertions is important, but it is quite easy to get it wrong. The assertion will fail as expected, but it will produce a confusing error message:<\/p>\n\n\n\n
assertEquals(\"actual\", \"expected\");\n\norg.junit.ComparisonFailure:\nExpected :actual\nActual :expected<\/code><\/pre>\n\n\n\nAssertJ helps you to write assertions that are much closer to natural language. This makes them more readable and reduces the chance of writing them wrongly:<\/p>\n\n\n\n
assertThat(\"actual\").isEqualTo(\"expected\");<\/code><\/pre>\n\n\n\nAnother benefit of AssertJ is the fluent interface which enables the chaining of multiple assertions. Instead of writing multiple statements, you can write it like this:<\/p>\n\n\n\n
assertThat(\"Foo\")\n .isNotNull()\n .startsWith(\"F\")\n .endsWith(\"o\")\n .contains(\"x\")\n .isEqualToIgnoringCase(\"foo\");<\/code><\/pre>\n\n\n\nThis will fail with a helpful message:<\/p>\n\n\n\n
java.lang.AssertionError:\n Expecting:\n <\"Foo\">\n to contain:\n <\"x\"><\/code><\/pre>\n\n\n\nBuilt-in assertions<\/h2>\n\n\n\n
AssertJ provides built-in assertions for many different types of objects. We\u2019ve already seen assertions on String objects. Here is an example of an assertion on integers:<\/p>\n\n\n\n
assertThat(123)\n .isGreaterThan(122)\n .isLessThan(124)\n .isBetween(100, 200);<\/code><\/pre>\n\n\n\nAssertions on lists are quite powerful \u2013 this example shows how to filter a list of User objects on the user role and extract user names (using Java 8 features):<\/p>\n\n\n\n
assertThat(users)\n .filteredOn(user -> user.getRole().equals(\"ADMIN\"))\n .extracting(User::getName)\n .contains(\"user1\", \"user2\");<\/code><\/pre>\n\n\n\nAssertions on exceptions are also supported:<\/p>\n\n\n\n
assertThatThrownBy(() -> { throw new RuntimeException(\"error\"); })\n .isInstanceOf(RuntimeException.class)\n .hasMessageContaining(\"error\");<\/code><\/pre>\n\n\n\nCustom assertions<\/h2>\n\n\n\n
It\u2019s also possible to write your own assertions \u2013 this is especially useful for your core domain model classes. You can write custom assertions manually or use the provided assertions generator. This will result in a domain specific language for use in tests. An example usage of custom assertions:<\/p>\n\n\n\n
assertThat(user)\n .hasRole(\"ADMIN\")\n .hasName(\"user1\");<\/code><\/pre>\n\n\n\nInstallation<\/h2>\n\n\n\n
If you want to try the AssertJ library, you can get it via Maven:<\/p>\n\n\n\n
<dependency>\n <groupId>org.assertj<\/groupId>\n <artifactId>assertj-core<\/artifactId>\n <version>3.11.1<\/version>\n <scope>test<\/scope>\n<\/dependency><\/code><\/pre>\n\n\n\nOr if you use Gradle:<\/p>\n\n\n\n
testCompile(\"org.assertj:assertj-core:3.11.1\")<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"