Nifty JUnit : Using Rule on Method and Class level

Willem CheizooMarch 14th, 2015Last Updated: March 12th, 2015

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As shown in a the post Nifty JUnit : Working with temporary files, it is possible to use @Rule in a JUnit test, which is a Method level Rule. In this example I would like to show the variation of the @ClassRule for a Class level Rule.

Method Rule

The @Rule is fired before each test method (just like @Before) and after each test method (just like @After) of the test class, as shown in the example below.

JUnitRuleTest

package com.jdriven;
 
import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.TemporaryFolder;
 
import java.io.File;
import java.io.IOException;
 
public class JUnitRuleTest {
 
    //The Folder will be created before each test method and (recursively) deleted after each test method.
    @Rule
    public TemporaryFolder temporaryFolder = new TemporaryFolder();
 
    @Test
    public void testJUnitRule() throws IOException {
        File tempFile = temporaryFolder.newFile("tempFile.txt");
 
        //Your test should go here.
    }
}

Class Rule

Besides the regular @Rule we have the possibility to create a @ClassRule. In the example of the TemporaryFolder it will result in a folder which is created before all test methods (just like @BeforeClass) and destroyed after all test methods (just like @AfterClass). In the example below you can create a temporary file and use the exact same file in all the test methods. The temporary file will be deleted when all the test methods are finished.

JUnitClassRuleTest

package com.jdriven;
 
import org.junit.BeforeClass;
import org.junit.ClassRule;
import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.TemporaryFolder;
 
import java.io.File;
import java.io.IOException;
 
public class JUnitClassRuleTest {
 
    //The Folder will be (recursively) deleted after all test.
    @ClassRule
    public static TemporaryFolder temporaryFolder = new TemporaryFolder();
 
    public static File tempFile;
 
    @BeforeClass
    public static void createTempFile() throws IOException {
        tempFile = temporaryFolder.newFile("tempFile.txt"); //The tempFile will be deleted when the temporaryFolder is deleted.
    }
 
    @Test
    public void testJUnitClassRule_One() {
        //Your test should go here, which uses tempFile
    }
 
    @Test
    public void testJUnitClassRule_Two() {
        //Your test should go here and uses the same tempFile
    }
}