Assert an object is a specific type

Question

Is it possible in JUnit to assert an object is an instance of a class  For various reasons I have an object in my test that I want to check the type of  Is it a type of Object1 or a type of Object2   Currently I have   assertTrue myObject instanceof Object1   assertTrue myObject instanceof Object2     This works but I was wondering if there is a more expressive way of doing this   For example something like   assertObjectIsClass myObject  Object1     I could do this   assertEquals myObject class  Object1 getClass       Is there a specific assert method that allows me to test a type of an object in a more elegant  fluid manner

User · Answer

Solution for JUnit 5

The documentation says:

However, JUnit Jupiter’s org.junit.jupiter.Assertions class does not provide an assertThat() method like the one found in JUnit 4’s org.junit.Assert class which accepts a Hamcrest Matcher. Instead, developers are encouraged to use the built-in support for matchers provided by third-party assertion libraries.

Example for Hamcrest:

import static org.hamcrest.CoreMatchers.instanceOf;
import static org.hamcrest.MatcherAssert.assertThat;

import org.junit.jupiter.api.Test;

class HamcrestAssertionDemo {

    @Test
    void assertWithHamcrestMatcher() {
        SubClass subClass = new SubClass();
        assertThat(subClass, instanceOf(BaseClass.class));
    }

}

Example for AssertJ:

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

import org.junit.jupiter.api.Test;

class AssertJDemo {

    @Test
    void assertWithAssertJ() {
        SubClass subClass = new SubClass();
        assertThat(subClass).isInstanceOf(BaseClass.class);
    }

}

Note that this assumes you want to test behaviors similar to instanceof (which accepts subclasses). If you want exact equal type, I don’t see a better way than asserting the two class to be equal like you mentioned in the question.

User · Answer

Solution for JUnit 5 for Kotlin   Example for Hamcrest   import org hamcrest CoreMatchers import org hamcrest MatcherAssert import org junit jupiter api Test  class HamcrestAssertionDemo         Test     fun assertWithHamcrestMatcher             val subClass   SubClass           MatcherAssert assertThat subClass  CoreMatchers instanceOf lt Any gt  BaseClass  class java              Example for AssertJ   import org assertj core api Assertions assertThat import org junit jupiter api Test  class AssertJDemo         Test     fun assertWithAssertJ             val subClass   SubClass           assertThat subClass  isInstanceOf BaseClass  class java

User · Answer

You can use the assertThat method and the Matchers that comes with JUnit   Take a look at this link that describes a little bit about the JUnit Matchers   Example   public class BaseClass      public class SubClass extends BaseClass       Test   import org junit Test   import static org hamcrest CoreMatchers instanceOf  import static org junit Assert assertThat           author maba  2012-09-13     public class InstanceOfTest         Test     public void testInstanceOf             SubClass subClass   new SubClass            assertThat subClass  instanceOf BaseClass class

User · Answer

Since assertThat which was the old answer is now deprecated  I am posting the correct solution   assertTrue objectUnderTest instanceof TargetObject

[java] Assert an object is a specific type

Solution for JUnit 5

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