JUnit

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jUnit

In eclipse, create a source folder to store content of testing classes. Name it "test". In project properties go to Build Path, Add Library, jUint
Make a new jUnit Test Case, jUnit 4,

@Before Any method annotated, will be executed before performing any of the test methods. //to allocate resources
@After Any method annotated, will be executed after performing any of the test methods. //to release resources
@Test Any method annotated, will be executed as a test case.
@Ignore Test will be ignored
@BeforeClass for all tests
@AfterClass for all tests

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

public class TestHelloWorldPrompt {

    @Test
    public void testX(){
        HelloWorld h = new HelloWorld();
        assertEquals("my message a", "Hello World", h.say());
    }
}

if you have a method that is meant to output to a file, don't pass in a filename, or even a FileWriter. Instead, pass in a Writer. That way you can pass in a StringWriter to capture the output for testing purposes. Then you can add a method (e.g. writeToFileNamed(String filename)) to encapsulate the FileWriter creation.

Test Constructors (when there are multiple)

@Test
public void testCreate() {
assertEquals(23, new MyClass(23).getX());
}

@Test(expected = IndexOutOfBoundsException.class)
    public void arraySizeTest() {
        ArrayList arr = new ArrayList();
        arr.get(0);
    }

To test private methods, you can use reflection to subvert the access control mechanism with the aid of the PrivilegedAccessor. For details on how to use it, read this article.

jUnit executes each test within a separate instance of the test class. It reports failure on each test.

You can add a @BeforeClass annotation to a method to be run before all the tests in a class, and a @AfterClass annotation to a method to be run after all the tests in a class.

Access Private Fields. methods, constructors

Link

class FieldTest {
    public String publicString = "Foobar";
    private String privateString = "Hello, World!";
}
------------------------------
import java.lang.reflect.Field;

public class Test6 {
  public static void main(String args[])
    throws Exception {
    final Field fields[] =
        FieldTest.class.getDeclaredFields();
    for (int i = 0; i < fields.length; ++i) {
      if ("privateString".equals(fields[i].getName())) {
        fields[i].setAccessible(true);
        System.out.println(
            fields[i].get(new FieldTest()));
        break;
      }
    }
  }
}

PrivateAccessor to check the value of private fields in unit testing.

import java.lang.reflect.Field;
import junit.framework.Assert;

/**
 * Provides access to private members in classes.
 */
public class PrivateAccessor {
  public static Object getPrivateField (Object o,
  String fieldName) {
    /* Check we have valid arguments */
    Assert.assertNotNull(o);
    Assert.assertNotNull(fieldName);
    /* Go and find the private field... */
    final Field fields[] =
        o.getClass().getDeclaredFields();
    for (int i = 0; i < fields.length; ++i) {
      if (fieldName.equals(fields[i].getName())) {
        try {
          fields[i].setAccessible(true);
          return fields[i].get(o);
        } catch (IllegalAccessException ex) {
          Assert.fail ("IllegalAccessException accessing " +
            fieldName);
        }
      }
    }
    Assert.fail ("Field '" + fieldName +
                 "' not found");
    return null;
  }
}

Handle Hard-to-Control Sources for Testing

Use an interface for that resource as a type, and use an easily implemented (simulated) resource for test purposes. replace it with real resource when necessary, as a field (data) assignment. You can pass this resource in constructor or ...
Wrap it in another object and use and maintain that ibject for proper context of use