What about Hamcrest?

Hamcrest is a powerful library for writing custom matchers. Although FEST-Assert and Hamcrest have similar goals, FEST-Assert takes a different approach. Here is an example using Hamcrest (borrowed from Martin Gilday's example posted at the TestNG mailing list):

import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.containsString;
import static org.hamcrest.Matchers.equalTo;
import static org.testng.Assert.assertTrue;
 
import org.testng.annotations.Test;
 
public class SomeTest {
 
  @Test public void withHamcrest() {
    assertTrue(true);
    int result = 2 + 3;
    assertThat("calculation", 5, equalTo(result));
    assertThat("Hello World", containsString("World"));
  }
}

This is the same example, using FEST's assertions:

import static org.fest.assertions.Assertions.assertThat;
 
import org.testng.annotations.Test;
 
public class SomeTest {
 
  @Test public void testApp() {
    assertThat(true).isTrue();
    int result = 2 + 3;
    assertThat(result).as("calculation").isEqualTo(5);
    assertThat("Hello World").contains("World");
  }
}

We like FEST-Assert's approach because:

1. Only one static import is needed (org.fest.assertions.Assertions.assertThat)
2. Allows us to use our IDE's "auto-complete" feature: we only type "." and we get the possible assertion methods for the value passed to "assertThat"
3. We can chain related assertion methods:

   assertThat(yoda).isInstanceOf(Jedi.class)
                   .isEqualTo(foundJedi)
                   .isNotEqualTo(possibleSith);

Which one to use? Hamcrest or FEST-Assert? It is up to you...it depends on the needs of your project and your coding style!