AssertJ is a library providing easy to use rich typed assertions
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AssertJ - Fluent assertions for java

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AssertJ provides a rich and intuitive set of strongly-typed assertions to use for unit testing (either with JUnit or TestNG).

The AssertJ web site contains all projects documentation and can be here, it notably inlcudes AssertJ Core documentation.

You can ask questions and make suggestions on AssertJ google group.

AssertJ's goals

AssertJ's ambition is to provide a rich and intuitive set of strongly-typed assertions to use for unit testing.
The idea is that, when writing unit tests, we should have at our disposal assertions specific to the type of the objects we are checking. If you're checking the value of a String, you use String-specific assertions. Checking the value of a Map? Use the Map-specific assertions, which make it easy to check on the contents of the map.

AssertJ is composed of several modules:

Assertion missing? Please create an issue!

AssertJ's assertions are super easy to write: just type assertThat followed by the actual value in parentheses and then a dot, and any Java IDE will show you all the assertions available for the type of the object to verify. No more confusion about the order of the "expected" and "actual" values. Our assertions are very readable as well: they read very close to plain English, making it easier for non-technical people to read test code. A lot of effort have been done to provide intuitive error messages showing as clearly as possible what the problem is.

Note that AssertJ 2.x requires at least Java 7 and AssertJ 3.x requires at least Java 8.

AssertJ core javadoc is published here.

Latest News

To read details on the latest releases, please go to AssertJ Core latest news.


It is easy to start using AssertJ, follow the One minute starting guide.

Assertions for your own custom types

Having assertions for common types like List is great, but you might want some that are specific to your own types. This is possible with AssertJ because it is easily extensible so it's simple to write assertions for your custom types.

Moreover, to ease your work, we provide assertions generator that can take a set of custom types and create specific assertions. The tools provided are:

Replacing JUnit assertions by AssertJ Assertions

To help you replace JUnit assertions by AssertJ ones, you can use a script or do regexp search and replace manually as indicated here.

Migrating from FEST Assertions

Check our migration guide, it covers migrating from Fest 1.4 and migrating from Fest 2.x.

Want to contribute?

You are encouraged to contribute any missing, useful assertions. To do so, please read the contributors section.