JUnit Tests

import static org.junit.jupiter.api.Assertions.assertEquals;
import org.junit.jupiter.api.Test;

public class SquareTest{

    @Test
    public void testSquareConstructorShouldSetLength(){
        Square square = new Square(2.0);
        assertEquals(2.0, square.getLength());
    }
}

Install Parameters Library

dependencies {
    // Use JUnit Jupiter API for testing.
    testImplementation 'org.junit.jupiter:junit-jupiter-api:5.6.2', 
        'org.hamcrest:hamcrest:2.2', 
        'org.junit.jupiter:junit-jupiter-params'

    // Use JUnit Jupiter Engine for testing.
    testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine'

    // This dependency is used by the application.
    implementation 'com.google.guava:guava:29.0-jre'
}

JUnit Parameterized Tests

import static org.junit.jupiter.api.Assertions.assertEquals;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.ValueSource;

public class StoveTest{

    @ParameterizedTest
    @ValueSource(doubles = {1.0, 2.1, 3.2, 4.3, 5.9})
    public void SetSquareLengthToPositiveValue(double setting){
        Square square = new Square(setting);
        assertEquals(setting, square.getLength());
    }
}

JUnit Assertions

• assertTrue | assertFalse
• assertEquals | assertNotEquals
• assertArrayEquals
• assertLinesMatch
• assertNull | assertNotNull
• assertSame | assertNotSame

Catching Exceptions

@Test
void exceptionTesting() {
    Exception exception = assertThrows(
        IllegalArgumentException.class, 
        () -> new Square(-1.0));
    assertEquals("Length cannot be negative", 
        exception.getMessage());
}

Checking Output

@Test 
public void testHelloWorldMain() {
    HelloWorld hw = new HelloWorld();

    final PrintStream systemOut = System.out;
    ByteArrayOutputStream testOut = new ByteArrayOutputStream();
    System.setOut(new PrintStream(testOut));

    hw.main(new String[]{});

    System.setOut(systemOut);

    assertEquals(testOut.toString(), "Hello World\n");
}