JUnit

What is JUnit?

JUnit is a simple framework to write repeatable tests.

A typical JUnit 4.x test consists of multiple methods annotated with the @Test annotation.

At the top of every JUnit test class, we should include all the static Assert methods and annotations like so:

import static org.junit.Assert.*;
import org.junit.Test;
import org.junit.Before;
import org.junit.After;

Use the @Before to annotate initialization methods that are run before every test and @After to annotate break-down methods that are run after every test.

Each test method should test one thing, and the method name should reflect the test’s purpose. For example:

public void toStringYieldsTheStringRepresentation() {
       String[] array = {"a", "b", "c"};
       ArrayWrapper<String> arrayWrapper = new ArrayWrapper<String>(array);
       assertEquals("[a, b, c]", arrayWrapper.toString());
}

Hamcrest

In more recent versions (JUnit 4.4+), JUnit also includes Hamcrest matchers:

import static org.hamcrest.Matchers.*;
import static org.junit.Assert.*;

Then you can create more readable tests using the Hamcrest core-matchers. For example:

@Test
public void sizeIs10() {
     assertThat(wrapper.size(), is(10));
}

Assumptions

Often, there are variables outside of a test that is beyond your control. But the test ...