Test-Driver-Development

Test Driver Development | Java | Maven | JUnit

Introduction

Test Driven Development (TDD) is development approach in which

Test cases are developed first to test and validate all the use cases.
Initially, all the test cases are going to fail as there isn't any code to support it.
Then we will be writing our code.
Few test cases will start to pass.
We will write more code and eventually all case test will get passed.
We will be refactoring our code a little more and will test again.

In simple terms, test cases for each functionality are created and tested first
and if the test fails then the new code is written in order to pass the test and making code simple and bug-free.

Benefits of TDD

Better code quality - We define the expecatations/use cases and then code accordingly. This helps to write a focused code.
Error prone code - It helps to create an error prone code as in each stage, we check if our test cases are not failing.
Ease of maintenance - Changes to the applications will be easier and it will ensure that the existing functionality is working as expected.
Save overall project cost in long run

Problem Statement: String Calculator

I used the following problem statement to create this TDD java application: https://osherove.com/tdd-kata-1
String Calculator

Create a simple class StringCalculator with a method public int add(string numbers)
The method can take 0, 1 or 2 numbers, and will return their sum
(for example: for an empty string it will return 0)
“” == 0 , “1” == 1 , “1,2” == 3

Add function:

Link to the function

Snapshot of add function

   public int add(String numbers) throws NegativeNumberException {
       instance().incrementCounter();

   	if (numbers == null || numbers.trim().isEmpty())
   		return 0;

   	// remove '\n' and '//'
   	// split on ',' or ';'
   	String numberList[] = numbers.replaceAll("[\n//*\\[\\]%]+", ",").split(",|;");

   	int res = 0;
   	List<String> negativeNum = new ArrayList<>();
   	for (String num : numberList) {

   		if (num.contains("-")) {
   			negativeNum.add(num);
   		} else if (!num.trim().isEmpty())
   			res += (Integer.parseInt(num) < 1000 ? Integer.parseInt(num) : 0);
   	}

   	if (!negativeNum.isEmpty()) {
   		throw new NegativeNumberException("negatives not allowed" + negativeNum);
   	}

   	return res;
   }