Skip to main content
For more updates follow@AkashSingh3031.
PrepVerseDocs

Testing with JUnit and Build Tools (Maven and Gradle)

Build tools​

ToolConfig fileNotes
Mavenpom.xmlConvention over configuration; huge ecosystem
Gradlebuild.gradle(.kts)Flexible, fast incremental builds
<project>
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.prepverse</groupId>
  <artifactId>notes</artifactId>
  <version>1.0.0</version>

  <properties>
    <maven.compiler.release>21</maven.compiler.release>
  </properties>

  <dependencies>
    <dependency>
      <groupId>org.junit.jupiter</groupId>
      <artifactId>junit-jupiter</artifactId>
      <version>5.10.2</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
</project>
mvn clean test       # compile and run tests
mvn package          # build the jar

Standard layout: src/main/java, src/main/resources, src/test/java.

JUnit 5 tests​

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

class CartTest {
    private Cart cart;

    @BeforeEach
    void setUp() { cart = new Cart(); }

    @Test
    void emptyCartHasZeroTotal() {
        assertEquals(0.0, cart.total(), 0.0001);
    }

    @Test
    void addsItemPrices() {
        cart.add(new Item("pen", 10));
        cart.add(new Item("book", 25));
        assertEquals(35.0, cart.total(), 0.0001);
    }

    @Test
    void rejectsNegativePrice() {
        assertThrows(IllegalArgumentException.class, () -> new Item("x", -1));
    }
}

Parameterised tests​

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

class MathTest {
    @ParameterizedTest
    @CsvSource({"1,2,3", "0,0,0", "-5,5,0"})
    void adds(int a, int b, int expected) {
        assertEquals(expected, a + b);
    }
}

Mocking with Mockito​

import static org.mockito.Mockito.*;

class OrderServiceTest {
    @Test
    void chargesThePaymentGateway() {
        PaymentGateway gateway = mock(PaymentGateway.class);
        when(gateway.charge(anyDouble())).thenReturn(true);

        OrderService service = new OrderService(gateway);
        assertTrue(service.checkout(49.99));

        verify(gateway).charge(49.99);
    }
}

Testing guidelines​

  • Test behaviour, not implementation details; keep tests fast and independent.
  • Name tests by the scenario and expected outcome.
  • Mock only boundaries (network, database, clock), not your own simple classes.
  • Run tests in CI on every push (see Testing and deployment).
Previous
Design Patterns in Java
Next
JDBC and Persistence in Java
Loading Comments...