Test Driven Development
The 3 Fundamental Test Clauses

Fundamental Clauses

• There exists an inferrable
• given,
• when,
• and then
• clause for every test.

Fundamental Clauses: given

• The given clause declares, initializes, and instantiates all known variable values.
• The given clause of a test sets the state of the “environment” for the entity that needs to be tested.
• The expected output is always given prior to testing. (How else could one test?)
• An object must set its state for the respective test
  • A Person must setName before attempting to getName
  • An Inventory must add items before attempting to get an item
  • A Game must have a Player before attempting to play

Fundamental Clauses: given

Example 1

• A Person must setName before attempting to getName

@Test
public void testGetName() {
    // given
    Person person = new Person();
    String expectedName = "Leon";
    person.setName(expectedName);
}

Fundamental Clauses: given

Example 2

• An Inventory must add items before attempting to get an item

@Test
public void testGetItem() {
    // given
    Inventory inventory = new Inventory();
    String expectedItem = "Milk";
    inventory.add(expectedItem)
}

Fundamental Clauses: given

Example 3

• A Game must add a Player before attempting to play

  @Test
  public void testGetWinner() {
    // given
    Game game = new Game();
    Player expectedWinner = new Player();
    game.add(player);
    game.play();
  }
  

Fundamental Clauses: when

• when clause invokes the method to be tested
• when clause stores output of method invokation.
  • void methods should change state of an object.
  • output should be retrieved by supplementary method-invokation followed by the invokation of the method to be tested.
  • by convention, the output of the method invokation is stored in a variable named actual.

Fundamental Clauses: when

• In simple test-classes, test-methods are named after the method to be tested in the when clause.
  • The getName method of a Person class is tested by testGetName method of a PersonTest class.
  • The get method of an Inventory class is tested by testGet method of a InventoryTest class.
  • The play method of a Game class is tested by testPlay method of a GameTest class.

Fundamental Clauses: when

Example 1

@Test
public void testGetName() {
    // given
    Person person = new Person();
    String expectedName = "Leon";
    person.setName(expectedName);

    // when
    String actualName = person.getName();
}

Fundamental Clauses: when

Example 2

@Test
public void testGetItem() {
    // given
    Inventory inventory = new Inventory();
    String expectedItem = "Milk";
    inventory.add(expectedItem)

    // when
    String expectedItem = inventory.get(0);
}

Fundamental Clauses: when

Example 3

@Test
public void testGetWinner() {
    // given
    Game game = new Game();
    Player expectedWinner = new Player();
    game.add(player);
    game.play();

    // when
    Player actualWinner = game.getWinner()
}

Fundamental Clauses: then

• then clause will assert something to be true regarding the output of the method being tested
  • If these assertions fail, then we will be pointed to the defect in the code.
  • If these assertions pass, then we know our implementation works as expected.
• Simple test cases typically assert the expected output to be equal to the actual output.

Fundamental Clauses: then

Example 1

@Test
public void testGetName() {
    // given
    Person person = new Person();
    String expectedName = "Leon";
    person.setName(expectedName);

    // when
    String actualName = person.getName();

    // then
    Assert.assertEquals(expectedName, actualName);
}

Fundamental Clauses: then

Example 2

@Test
public void testGetItem() {
    // given
    Inventory inventory = new Inventory();
    String expectedItem = "Milk";
    inventory.add(expectedItem)

    // when
    String actualItem = inventory.get(0);

    // then
    Assert.assertEquals(expectedItem, actualItem);
}

Fundamental Clauses: then

Example 3

@Test
public void testGetWinner() {
    // given
    Game game = new Game();
    Player expectedWinner = new Player();
    game.add(player);
    game.play();

    // when
    Player actualWinner = game.getWinner()

    // then
    Assert.assertEquals(expectedWinner, actualWinner)
}