Test-Driven Development with Unit Tests

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Why unit testing? 🔗

Practical reasons

Most programmers rely on tests.
For example, Microsoft assigns one tester per developer.
You may work as a tester.

A divide-and-conquer approach

Split the system into units for testing.
Debug each unit separately.
Identify where bugs may exist.
Avoid having to trace a bug through other units.

Test suites 🔗

A collection of test cases used to check that software behaves correctly.

Ad-hoc testing

Developers test whatever comes to mind.

Test suite

Test cases are defined in advance and executed.

Test framework

A program that executes test suites.
Examples include JUnit and TestNG.

Regression testing 🔗

Checking that existing functionality still works after software changes.

Changes may include enhancements, patches, or configuration updates.

Regression testing is essential for a stable and maintainable codebase.

Drivers and stubs in testing 🔗

Driver

Runs tests and collects results.
Supplies test cases to the unit under test, then receives and analyzes the results.

Stub

A fake object used when the unit under test interacts with other units.
Supplies the simple responses the unit under test needs in place of a real module.

JUnit 🔗

A unit-testing framework for the Java programming language.

A test case is an individual test of one method.
A test suite is a collection of test cases.

Unit tests play an important role in an agile approach.

Code often needs refactoring to reflect changes.
Unit tests ensure that the refactored code continues to work.

JUnit methods 🔗

Method	Description
assertEquals(expected, actual)	Checks that two values are equal
assertTrue(condition)	Checks that a condition is true
assertFalse(condition)	Checks that a condition is false
assertNull(object)	Checks that an object is null
assertNotNull(object)	Checks that an object is not null
assertSame(expected, actual)	Checks that two references point to the same object
assertNotSame(expected, actual)	Checks that two references point to different objects

Caution

Java provides x.equals(y) for comparing objects.

It works well for String and several other Java classes.

Define equals for objects of your own classes.

public boolean equals(Object obj) { ... }

The argument must have type Object. Since that is not the desired concrete type, cast it to the correct type, such as Person.

public boolean equals(Object something) {
		Person p = (Person)something;
		return this.name == p.name; // 원하는 대로 비교할 수 있다.
}

JUnit test case example 🔗

Traditional test case 🔗

/** IMath 클래스를 테스트하는 클래스이다. */
public class IMathTestNoJUnit {
    /** 테스트를 실행한다. */
    public static void main(String[] args) {
        printTestResult(0);
        printTestResult(1);
        printTestResult(2);
        printTestResult(3);
        printTestResult(4);
        printTestResult(7);
        printTestResult(9);
        printTestResult(100);
    }
 
    private static void printTestResult(int arg) {
        System.out.print("isqrt(" + arg + ") ==> ");
        System.out.println(IMath.isqrt(arg));
    }
}
 
// 실행 결과
// isqrt(0) ==> 0
// isqrt(1) ==> 1
// isqrt(2) ==> 2
// isqrt(3) ==> 2
// isqrt(4) ==> 2
// isqrt(7) ==> 3
// isqrt(9) ==> 3
// isqrt(100) ==> 10

JUnit test case 🔗

import org.junit.Test;
import static org.junit.Assert.assertEquals;
 
public class IMathTest extends TestCase{
		@Test
		public void testIsqrt() {
				assertEquals(0, IMath.isqrt(0));
				assertEquals(1, IMath.isqrt(1));
				assertEquals(2, IMath.isqrt(2));
				assertEquals(2, IMath.isqrt(3));
				assertEquals(2, IMath.isqrt(4));
				assertEquals(3, IMath.isqrt(7));
				assertEquals(3, IMath.isqrt(9));
				assertEquals(10, IMath.isqrt(100));
		}
}
 
// 실행 결과
// 테스트 케이스가 성공하면 아무것도 출력되지 않음
 
// 테스트 케이스가 실패하면 다음과 같이 출력됨
// java.lang.AssertionError: expected:<0> but was:<1>

JUnit exercise 🔗

Test the following code using JUnit.

public class ForYou {
	public static int min(int x, int y){
		if(x < y) return x;
		else return y;
	}
}

Answer 🔗

import org.junit.Test;
import static org.junit.Assert.assertEquals;
 
public class ForYouTest extends TestCase{
		@Test
		public void testMin() {
				assertEquals(1, ForYou.min(1, 2));
				assertEquals(1, ForYou.min(2, 1));
				assertEquals(0, ForYou.min(0, 0));
				assertEquals(-1, ForYou.min(-1, 0));
				assertEquals(-1, ForYou.min(0, -1));
		}
}

Fixtures 🔗

Code you want to run before or after a test case.

Obtain a fixture by overriding methods.

protected void setUp() { ... }
protected void tearDown() { ... }

Test execution rules:

protected void runTest() {
    setUp();
    // <run the test>;
    tearDown();
}

The structure of test methods 🔗

A test method returns no result.
If a test succeeds, the method takes no further action.
If it fails, it throws AssertionFailedError.
The JUnit framework catches and handles this error, so you do not need to handle it separately.

Test-Driven Development with Unit Tests | PromleeBlog