🖐 5 TDD Most Common Mistakes

If you are using TDD, as you should be 🤨, you have been a victim of at least one of those anti-patterns.

We will discuss 5 🖐 of them, looking at their Causes, Problems and how to avoid them.

1️⃣ The Liar 🤥

Passes all tests with no useful assertions

• Causes
  • Chasing test coverage
• Problem
  • Illusiuon of coverage
  • Waste of time and money
• Correction
  • Delete the tests

    @Test
    public void liarTest(){
        ShipmentService shipmentService = new ShipmentService();
        shipmentService.doStuff();
        assertTrue(true);
    }

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2️⃣ Excessive Setup 🧰

Requires a lot of work to prepare the test

• Causes
  • Poor modularity and poor separation of concerns in the design
• Problem
  • Tests and code are highly coupled
  • Hard to maintain
  • This will slow down the development to a halt
• Correction
  • Improve abstraction and separation of concerns in the code
  • Write pure functions

    @Test
    public void excessiveSetup (){
        // set up beginning
        VerificationService verificationService = new VerificationService();
        ShipmentRepository shipmentRepository = new ShipmentRepository();
        ShipmentService shipmentService = new ShipmentService(verificationService, shipmentRepository);

        Product product = new Product("Product");
        Owner owner = new Owner("owner");
        Count count = new Count(100);
        Shipment shipment = new Shipment(product, owner, count);
        ShipmentDetail shipmentDetail = new ShipmentDetail(shipment);
        // set up ending

        // rest of test
    }

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3️⃣ The Giant 💥

Has multiple assertions in a single test

• Causes
  • Testing too much things at the same time

• Problem

  • Hard to understand
  • Test and code are highly coupled
  • Hard to maintain

• Correction

  • Decompse the test into multiple tests

    @Test
    public void theGiant (){
        ShipmentService shipmentService = new ShipmentService();

        Shipment shipment = new Shipment("product", "owner", 2);
        shipmentService.processShipment_Free(shipment);
        assertEquals("productUpdated", shipment.getProduct());
        assertEquals("ownerUpdated", shipment.getOwner());
        assertEquals(5, shipment.getCount());

        Shipment shipment2 = new Shipment("product2", "owner2", 9);
        shipmentService.processShipment_Premium(shipment);
        ssertEquals("productPremium", shipment2.getProduct());
        assertEquals("ownerPremium", shipment2.getOwner());
        assertEquals(41, shipment2.getCount());

        // could go on even further
        //....
    }

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4️⃣ The Mockery 🤡

Uses so many mocks that the real code isn't tested

• Causes

  • Excessive setup

• Problems

  • Doesn't test anything

• Correction

  • Review code design
  • Improve abstraction and seperation of concerns

    @Test
    public void theMockery (){
        doReturn("test").when(serviceMock).getValue();
        doReturn(true).when(serviceMock).isValid();

        assertEquals("test", serviceMock.getValue());
        assertTrue(serviceMock.isValid());
    }

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5️⃣ The inspector 🧐

Adding functions that are only used in the tests

• Causes

  • Chasing test coverage

• Problems

  • Waste of time and money since it doesn't test production code

• Corrections

  • Delete those functions.

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The source of this information is mainly from this amazing YouTube video.