Chapter 3. Unit Tests with no Collaborators

3.3. Your First JUnit Test

Before you write a test, you need to have a list of test cases ready. You can write it down somewhere, if you feel it helps, but keeping it in your head should usually be enough.

Looking at the code of the Money class you will probably notice two things that can be tested:

•the constructor,

•the equals() method.

Testing of the constructor seems like a trivial matter, and this is exactly why we will start with it. The only thing we can check here is if amount and currency have been properly set4.

Listing 3.3. First JUnit unit test

import org.junit.Test;

import static org.junit..Assert.assertEquals;

public class MoneyTest {

@Test

public void constructorShouldSetAmountAndCurrency() { Money money = new Money(10, "USD");

assertEquals(10, money.getAmount()); assertEquals("USD", money.getCurrency());

}

}

@Test annotation is required, so JUnit (and other tools) will recognize this method as a test method. The static import of the Assert class method(s) makes assertion checking more concise.

The test class does not have to extend any base class or implement any interfaces. Its name is also not important, though using the Test suffix leaves no doubt as to its purpose.

The test method can take any name. An SUT is created.

The SUT is put to the test and the results are verified using the static assertEquals() methods of the Assert class.

That is quite a lot of information for such a simple class! Much more could be written about each line of this code, but that is enough for now. We will discuss it step by step in the course of considering subsequent examples. Let us run the test now.

There are many ways to run tests written with JUnit. Please consult Appendix B, Running Unit Tests, which contains detailed description of how to run tests with Eclipse, IntelliJ IDEA, Gradle and Maven.

After you have run this first test, JUnit will print a short summary. It might vary, depending on the way you run it (in particular, your IDE will probably present it in some nicer way), but it will always contain information about executed, passed and failed tests. An example is shown below:

4It is questionable whether such code is worth testing in code-first manner. Please see the discussion in Section 10.5.

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