Assert an object is a specific type

Turbocharge with assertThat and Matchers

Put the pedal to the metal in JUnit tests using Matchers and assertThat. It lets you don your Sherlock Holmes hat and investigate object types in style.

import static org.hamcrest.CoreMatchers.instanceOf;
import static org.junit.Assert.assertThat;

// ...

@Test
public void fireUpInstanceOfTest() {
    // Actual test, or a round of guessing game?
    assertThat(myObject, instanceOf(MyClass.class));
}


Replace multiple assertTrue or assertEquals statements with this one liner. Elegance? Check. Efficiency? Check. Confidence? Triple check!

JUnit 5: a bouquet with assertInstanceOf()

The assertInstanceOf() in JUnit 5 is like a rose among the thorns. It checks and returns the object in one fell swoop, saving you from casting nightmares.

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

// ...

@Test
void blazeInstanceOfTest() {
    // Treating objects with kindness and type-checking
    assertInstanceOf(MyClass.class, myObject);
}


When assertJ plays the fiddle

AssertJ struts about with a fluent interface, turning assertions into romantic strolls in the park:

import static org.assertj.core.api.Assertions.assertThat;

// ...

@Test
void sparkAssertJTypeCheck() {
    // Where AssertJ sings "Check Type-checked in 12 notes"
    assertThat(myObject).isInstanceOf(MyClass.class);
}


When there are thorny edge cases, AssertJ plays the tune.

Kotlin: force of assert

Kotlin assert charms with its brevity. Typecasting in Java? Pfft! Say hello to is -

import kotlin.test.assertTrue

// ...

@Test
fun kotlinRoastsJava() {
    // Swedish house mafias drop beats, Kotlin drops 'is'
    assertTrue(myObject is MyClass, "Not an instance of MyClass")
}


To make Kotlin and JUnit play together, add AssertionsJVM.kt to your beat.

Avoid expiration dates

Just like milk, practices too can go bad. Stay vigilant and say no to deprecated methods. Because, that's how codebases rot!

Unmasking the real identity

When you need to verify the object's exact type identity, not its ancestry:

// 'Who's your daddy?' becomes 'Who exactly ARE you?'
assertEquals(MyClass.class, myObject.getClass());


This ensures myObject's identity is a portrait-perfect match to MyClass, without dragging the family tree into this.