JUnit 4 Test Fixtures Examples

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JUnit 4 Tutorial

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1. Overview

A test fixture is a fixed state of a set of objects used as a baseline for running tests. The purpose of a test fixture is to ensure that there is a well known and the fixed environment in which tests are run so that results are repeatable. Examples of fixtures:

• Preparation of input data and setup/creation of fake or mock objects
• Loading a database with a specific, known set of data
• Copying a specific known set of files creating a test fixture will create a set of objects initialized to certain states.

JUnit provides annotations so that test classes can have fixture run before or after every test, or one time fixtures that run before and after only once for all test methods in a class.

There are four fixture annotations: two for class-level fixtures and two for method-level ones. At the class level, you have @BeforeClass and @AfterClass, and at the method (or test) level, you have @Before and @After.

2. JUnit 4 Test Fixtures Examples

Example 1:

public class CustomerTest {

  private Customer customer;
  private static final int ID = 1;
  private static final String FIRSTNAME = "Winston";
  private static final String LASTNAME = "Churchill";

  @BeforeEach
  public void setUp() {
    customer = new Customer(ID, FIRSTNAME, LASTNAME);
  }
}

Example 2:

package test;

import java.io.Closeable;
import java.io.IOException;

import org.junit.After;
import org.junit.AfterClass;
import org.junit.Before;
import org.junit.BeforeClass;
import org.junit.Test;

public class TestFixturesExample {
  static class ExpensiveManagedResource implements Closeable {
    @Override
    public void close() throws IOException {}
  }

  static class ManagedResource implements Closeable {
    @Override
    public void close() throws IOException {}
  }

  @BeforeClass
  public static void setUpClass() {
    System.out.println("@BeforeClass setUpClass");
    myExpensiveManagedResource = new ExpensiveManagedResource();
  }

  @AfterClass
  public static void tearDownClass() throws IOException {
    System.out.println("@AfterClass tearDownClass");
    myExpensiveManagedResource.close();
    myExpensiveManagedResource = null;
  }

  private ManagedResource myManagedResource;
  private static ExpensiveManagedResource myExpensiveManagedResource;

  private void println(String string) {
    System.out.println(string);
  }

  @Before
  public void setUp() {
    this.println("@Before setUp");
    this.myManagedResource = new ManagedResource();
  }

  @After
  public void tearDown() throws IOException {
    this.println("@After tearDown");
    this.myManagedResource.close();
    this.myManagedResource = null;
  }

  @Test
  public void test1() {
    this.println("@Test test1()");
  }

  @Test
  public void test2() {
    this.println("@Test test2()");
  }
}

Will Output something like the following:

@BeforeClass setUpClass
@Before setUp
@Test test2()
@After tearDown
@Before setUp
@Test test1()
@After tearDown
@AfterClass tearDownClass

Example 3

When you have a common fixture, here is what you do:

• Add a field for each part of the fixture
• Annotate a method with @org.junit.Before and initialize the variables in that method
• Annotate a method with @org.junit.After to release any permanent resources you allocated in setUp For example, to write several test cases that want to work with different combinations of 12 Swiss Francs, 14 Swiss Francs, and 28 US Dollars, first create a fixture:

public class MoneyTest { 
    private Money f12CHF; 
    private Money f14CHF; 
    private Money f28USD; 
    
    @Before public void setUp() { 
        f12CHF= new Money(12, "CHF"); 
        f14CHF= new Money(14, "CHF"); 
        f28USD= new Money(28, "USD"); 
    }
}

Example 4

import org.junit.*;
import static org.junit.Assert.*;
import java.util.*;
 
public class SimpleTest {
 
    private Collection<Object> collection;
 
    @Before
    public void setUp() {
        collection = new ArrayList<Object>();
    }
 
    @Test
    public void testEmptyCollection() {
        assertTrue(collection.isEmpty());
    }
 
 
    @Test
    public void testOneItemCollection() {
        collection.add("itemA");
        assertEquals(1, collection.size());
    }
}

Given this test, the methods might execute in the following order:

setUp()
testEmptyCollection()
setUp()
testOneItemCollection()
```

3. Conclusion

In this post, we have learned what is fixtures, it's usage and examples. There are four fixture annotations: two for class-level fixtures and two for method-level ones. At the class level, you have @BeforeClass and @AfterClass, and at the method (or test) level, you have @Before and @After. Read more on JUnit Developers Guide.

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JUnit 4 Tutorial

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