JUnit 5 File-Based Testing Setup | Generated by AI

Home 2025.08

Here’s a simplified setup using only JUnit 5 (without Mockito) for testing your algorithm solutions with input files (1.in):

1. Update pom.xml (JUnit Only)

<dependencies>
    <!-- JUnit 5 -->
    <dependency>
        <groupId>org.junit.jupiter</groupId>
        <artifactId>junit-jupiter-api</artifactId>
        <version>5.9.2</version>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>org.junit.jupiter</groupId>
        <artifactId>junit-jupiter-engine</artifactId>
        <version>5.9.2</version>
        <scope>test</scope>
    </dependency>
</dependencies>

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-surefire-plugin</artifactId>
            <version>3.0.0-M7</version>
        </plugin>
    </plugins>
</build>

2. Directory Structure

src/
├── main/
│   ├── java/com/algorithm/solutions/codeforces/CF123A.java  # Example solution
│   └── resources/codeforces/1.in                           # Input file
└── test/
    ├── java/com/algorithm/solutions/codeforces/CF123ATest.java  # Test class
    └── resources/codeforces/1.expected                         # Expected output (optional)

3. Example Test Class (CF123ATest.java)

package com.algorithm.solutions.codeforces;

import org.junit.jupiter.api.Test;
import java.io.*;

import static org.junit.jupiter.api.Assertions.*;

class CF123ATest {

    @Test
    void testWithInputFile() throws IOException {
        // Redirect stdin from src/test/resources
        InputStream originalIn = System.in;
        FileInputStream fileIn = new FileInputStream("src/test/resources/codeforces/1.in");
        System.setIn(fileIn);

        // Redirect stdout to capture output
        PrintStream originalOut = System.out;
        ByteArrayOutputStream outContent = new ByteArrayOutputStream();
        System.setOut(new PrintStream(outContent));

        // Run the solution
        CF123A.main(new String[0]);

        // Restore streams
        System.setIn(originalIn);
        System.setOut(originalOut);

        // Verify output (optionally compare with 1.expected)
        String output = outContent.toString().trim();
        assertTrue(output.endsWith("42"));  // Example assertion
    }
}

4. Key Features:

  1. Input Redirection
    • Reads 1.in from src/test/resources as System.in.
    • Uses ByteArrayOutputStream to capture System.out.
  2. Output Verification
    • Assert against expected output (or check key patterns).
  3. Clean Resource Handling
    • Restores original System.in/System.out after test.

5. Run Tests

mvn test

Or via IDE (IntelliJ/Eclipse/VSCode).

6. Alternative: Parameterized Tests (Multiple Inputs)

import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.CsvFileSource;

@ParameterizedTest
@CsvFileSource(resources = "/codeforces/test_cases.csv", numLinesToSkip = 1)
void testMultipleCases(String input, String expected) {
    System.setIn(new ByteArrayInputStream(input.getBytes()));
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    System.setOut(new PrintStream(out));

    CF123A.main(new String[0]);

    assertEquals(expected, out.toString().trim());
}

Create src/test/resources/codeforces/test_cases.csv:

input,expected
1 2 3,6
4 5 6,15

This gives you a lightweight testing setup with:

Let me know if you’d like to adapt this for a specific problem!

Back Donate