Java Unit Test Case: Asserting Expected method returns

Last update on March 13 2025 09:47:14 (UTC/GMT +8 hours)

Write a Java unit test case to assert that a given method returns the expected value.

Sample Solution:

Java Code:

// Calculator.java
public class Calculator {
    public int add(int a, int b) {
        return a + b;
    }
}

// CalculatorTest.java

import org.junit.Test;
import org.junit.runner.JUnitCore;
import org.junit.runner.Result;
import org.junit.runner.notification.Failure;

import static org.junit.Assert.assertEquals;

public class CalculatorTest {

    @Test
    public void testAdd() {
        // Arrange
        Calculator calculator = new Calculator();

        // Act
        int result = calculator.add(3, 5);

        // Assert
        assertEquals(8, result); // The expected value is 8
    }

    public static void main(String[] args) {
        Result result = JUnitCore.runClasses(CalculatorTest.class);

        // Check if there are any failures
        if (result.getFailureCount() > 0) {
            System.out.println("Test failed:");

            // Print details of failures
            for (Failure failure : result.getFailures()) {
                System.out.println(failure.toString());
            }
        } else {
            System.out.println("All tests passed successfully.");
        }
    }
}

Sample Output:

All tests passed successfully.

Explanation:

The above Java code is a JUnit test class (CalculatorTest) for testing a hypothetical "Calculator" class. The code uses JUnit's annotations and classes to define a test case and run the tests. Let break down the key components:

• Test Method:
• @Test Annotation: Indicates that the following method is a JUnit test case.
• Arrange: Sets up the test scenario, including creating an instance of the "Calculator" class.
• Act: Calls the "add()" method on the "Calculator" instance with specific input values (3 and 5).
• Assert: Uses the assertEquals method to verify that the result of the "add()" method is equal to the expected value (8).
• Main Method:
• JUnitCore.runClasses: Invokes JUnit to run all the test methods in the specified class (CalculatorTest.class).
• Result: Holds the result of the test execution, including information about passed and failed tests.
• Checking Failures: If there are failures, it prints a message indicating that the tests failed and provides details about each failure. Otherwise, it prints a success message.

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Java program to create a unit test that asserts a method returns the expected value when provided with a typical input.
• Write a Java program to implement a JUnit test that compares the output of a method with a precomputed result using assertEquals.
• Write a Java program to design a test case that uses assertions to compare complex objects for deep equality.
• Write a Java program to construct a unit test that validates a function's return value with a custom delta for floating-point comparisons.

Java Code Editor:

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