Getting Started with AssertJ and HamCrest Assertion Frameworks

AssertJ vs HamCrest Assertion Frameworks

What is AssertJ and HamCrest?

With assertions, validate if something is working correctly or not, one can validate the response to check the functionality of the component. There are two of the most popular Java assertion frameworks which are available in the market and also these are open source. AssertJ is Java library that provides an interface for writing assertions. Test code readability and make maintenance of tests easier are the main goals of it.

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It is not as much popular as Hamcrest, but its popularity has been growing very fast in the last few years. It is one of the well known Java frameworks used for writing tests used for writing matcher objects, which are logically equal to "assertions." Due to its high popularity, later ported to other programming languages like C++, C#, Python, ActionScript 3, Objective C, PHP, JavaScript, R, and Erlang.

How does it Work?

The working process is described below:

Add below dependency in your maven project in a pom.xml file.


   org.hamcrest

   java-hamcrest

   {version}

   test

Basic example -


import static org.hamcrest.MatcherAssert.assertThat;

import static org.hamcrest.Matchers.*;

import junit.framework.TestCase;

public class TeaTest extends TestCase {

 public void testEquals() {

   Tea yoursTea = new Tea("Ginger");

   Tea myTea = new Tea("Ginger");

   assertThat(yoursTea, equalTo(myTea));

 }

}

Syntax -


// Simple Assertions

assertThat(a, equalTo(b));


// Dates Assertions

assertThat(tomorrow, isAfter(today));


// List Assertions

assertThat(list, Matchers.<collection> allOf(CoreMatchers.hasItem("a"),

      CoreMatchers.not(CoreMatchers.hasItem("b"))

));
</collection


// Null Assertions

assertThat(a, nullValue());


// Assertions With a Custom Message

assertThat("Error", a, equalTo(b));

Getting Started with AssertJ and HamCrest

Add below dependency in your maven project in a pom.xml file.


 org.assertj

 assertj-core

 {version}

 test

Syntax -


// Simple Assertions

assertThat(a).isEqualTo(b);


// Dates Assertions

assertThat(tomorrow).isAfter(today);


// List Assertions

assertThat(list).       

      contains("a").

      doesNotContain("b");


// Null Assertions

assertThat(actual).isNull();


// Assertions With a Custom Message

assertThat(a).isEqualTo(b).overridingErrorMessage("Error");

AssertJ and Hamcrest Examples

Below are some examples which show the similarities and differences of the common assertions between both -


// Equality

assertThat(actual, equalTo(expected)); // Hamcrest

assertThat(actual).isEqualTo(expected); // AssertJ


// Null checking

assertThat(actual, nullValue()); // Hamcrest

assertThat(actual).isNull(); // AssertJ


// Boolean checks

assertThat(actual, is(true)); // Hamcrest

assertThat(actual).isTrue(); // AssertJ


// Double comparisons

assertThat(actualDouble, closeTo(expectedDouble, error)); // Hamcrest

assertThat(actualDouble).isCloseTo(expectedDouble, Offset.offset(offset)); // AssertJ


// Assume/Assumption (JUnit’s skipping behavior)

assumeThat(actual, equalTo(expected)); // Hamcrest

// n/a                           AssertJ


// Expect (fail-at-end)

// n/a                           Hamcrest

softly.assertThat(actual).isEqualTo(expected); //AssertJ

What are the benefits?

There are some benefits of these Java assertion frameworks which are defined below -

Quality of code
Easy to find bugs
Facilitates changes
Simplifies Integration
Debugging

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Why it is imporatant?

There are many key points which explained that why these frameworks matters.

Readability

Both frameworks feel more natural and are easily readable and understandable as compared to others. Let's take an example of assertion.


assertEquals(expected, actual);

The above is a common way, the expected value is passed as the first argument and the actual value is passed as the second argument. But this method is very confusing until one can get used to it. But in the case of these two frameworks, the actual value is passed the as the first argument and the expected value is passed as the second argument, which is the biggest hurdle to get over.


assertThat(actual, equalTo(expected)); // Hamcrest

assertThat(actual).isEqualTo(expected); // AssertJ

Better Failure Messages

Much better error messages. In most of the other frameworks, the problem is that the assertion error does not report the expected values and actual values. Let's see an example -


assertTrue(expected.contains(actual));

java.lang.AssertionError

It doesn't provide the clearance of the error message but below code snippet provides a better explanation of an error which saves the time and hassle of a developer.


assertThat(actual, containsString(expected));

java.lang.AssertionError

Expected: a string containing abc

got: "def"

Custom Messages

Can also use assertions with custom messages in case of them. Can also pass any user-defined message. Let's take an example -


assertThat("Error", a, equalTo(b)); // Hamcrest

assertThat(a).isEqualTo(b).overridingErrorMessage("Error"); // AssertJ

Portability

In case of it, portability is also the advantage of its library. It can be used with both JUnit and Testing. Type Safety - Another advantage of these assertThat is that it is type-safe. It does not allow comparing of different types. Let's take an example -


assertEquals("abc", 123); //compiles, but fails

assertThat(123, is("abc")); //does not compile

How to adopt it?

Add the dependency according to the particular framework in pom.xml file.


// Hamcrest

   org.hamcrest

   java-hamcrest

   {version}

   test

// AssertJ

 org.assertj

 assertj-core

 {version}

 test

Import dependencies

Below are the basic examples -


// Hamcrest

@Test

   public void hamcrestTestExample() throws Exception {

       // Given

       Integer number = 5;

       // Then

       assertThat(number, greaterThan(3));

   }


// AssertJ

@Test

   public void assertJTestExample() throws Exception {

       // Given

       Integer number = 5;

       // Then

      assertThat(number).isGreaterThan(3);

   }

Concluding Assertion Frameworks

Hamcrest is much more popular as compared to AssertJ. But when we compare by commits, it has a more stable development pattern in the last years. On comparing the both Google Trends found that it is much more popular. The primary purpose is to tell about the most popular Java assertion frameworks available in the market. Can use any one of these two frameworks, to extend the capabilities of the standard assertions use any of the frameworks between these two. Each programming language has its libraries for assertions which help users to implement different kinds of assertions easily.