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Writing cleaner tests with Fluent Assertions

Fluent Assertions make tests highly readable and English-like, presenting a concise structure that simplifies comprehension

Your tests should be very easy to read essentially english like. There are multiple techniques to achieve this.

One of the ways is having fluent assertions. Fluent assertions are assertions chained together. The structure is such that it makes it more concise and easy to read.

We’ll take an example comparing Junit assertions with AssertJ assertions.

In the below example, we are checking if a Map contains specific keys, and if date is correct.

Map<String, String> jsonMessage = {someServiceCallReturningAJson};

// JUnit Assertions: Not Fluent
Set<String> expectedKeys = new HashSet<>(Arrays.asList("date", "userId", "randomField"));
Assertions.assertEquals(expectedKeys, jsonMessage.keySet());
Assertions.assertEquals("2001-07-04", jsonMessage.get("date"));

// AssertJ: Fluent Assertions
    .containsKeys("date", "userId", "randomField")
    .containsEntry("date", "2001-07-04");

The JUnit assertion is bulkier and will continue to get much bulkier with more assertion.

The AssertJ fluent assertion on other hand is grouped, contains helper methods that do not require specially conversion of object for common comparision.

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