Test-Driven Development: A walkthrough using Java

What
Is

TDD ?

Why Developers don't use at first?

"There is no time to write unit tests"

TDD

"Haven't used before and my code is good"

"It won't make my code bullet-proof"

Requires a paradigm shift

It's Simple but...

is not just about Testing.

TDD

Better structure in code

Reduce time debugging

Make a plan, then code

TDD

Best Practices.

Naming Conventions :

Place Test and Implementation in different packages.

Use descriptive names for methods.

public final void whenMoreThan2NumbersAreUsedThenExceptionIsThrown() {
        StringCalculator.add("1,2,3");
    }

Test

Processes:

Write tests before implementation code.
Rerun all tests every time implementation code changes.
All test should pass before new test is written.
Refactor only after all test are passing.

Development Practices:

Write simplest code to pass the test.

Assertions goes first.

Minimize assertions in each test

A practical example:

List of requirements to make a String Calculator:

Create a simple String calculator with a method int Add(string numbers)
The method can take 0, 1 or 2 numbers, and will return their sum (for an empty string it will return 0) for example “” or “1” or “1,2”
Allow the Add method to handle an unknown amount of numbers

Requirement 1:

The method can take up to 2 string numbers, each one separated by a comma(,)

class CalculatorTest extends groovy.util.GroovyTestCase {

    @Test(expected = RuntimeException.class)

    public final void whenMoreThan2NumbersAreUsedThrowException() {
        StringCalculator.add("1,2,3");
    }
    @Test
    public final void when2NumbersAreUsedDoNotThrowException() {
        StringCalculator.add("1,2");
        Assert.assertTrue(true);
    }
    @Test(expected = RuntimeException.class)
    public final void whenNonNumberIsUsedThenExceptionIsThrown() {
        StringCalculator.add("1,X");
    }


}

Test:

The method can take up to 2 string numbers, each one separated by a comma(,)

public class StringCalculator1 {
    public static final void add(final String numbers) {
        String[] numbersArray = numbers.split(",");
        if (numbersArray.length > 2) {
            throw new RuntimeException("Up to 2 numbers separated by comma (,) are allowed");
        } else {
            for (String number : numbersArray) {
                Integer.parseInt(number); // If it is not a number, parseInt will throw an exception
            }
        }
    }
}

Implementation:

Requirement 2:

@Test
public final void whenEmptyStringIsUsedThenReturnValueIs0() {
    Assert.assertEquals(0, StringCalculator.add(""));
}

Test

public static final int add(final String numbers) { // Changed void to int
    String[] numbersArray = numbers.split(",");
    if (numbersArray.length > 2) {
        throw new RuntimeException("Up to 2 numbers separated by comma (,) are allowed");
    } else {
        for (String number : numbersArray) {
            if (!number.isEmpty()) {
                Integer.parseInt(number);
            }
        }
    }
    return 0; // Added return
}

Implementation

For an empty string the method will return 0

TDD

Let's see

in action!

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What Is