In this tutorial we will dive into JUnit5 framework even more basing on simple Calculator project that will grow with us during tutorial.
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The tutorial repository can be found here: https://gitlab.eufus.eu/bpogodzinski/ach-tutorials/-/tree/TDD-java/TDD-java/Calculator |
Project Structure:
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.
├── pom.xml
└── src
├── main
│ └── java
│ └── Calculator.java
└── test
└── java
└── CalculatorTest.java
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public class Calculator {
static Double divide(Double a, Double b) {
if (b != 0) {
return a / b;
}
else{
throw new ArithmeticException("Division by 0 is impossible!");
}
}
public static void main(String[] args) {
System.out.printf(Calculator.divide(8.0,2.0).toString());
}
} |
As you can see it has only divide() method, that checks if b is equal to 0. If it is, it throws an exception.
So let's write first simple test:
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@Test
@DisplayName("Divide two finite numbers")
void divideTest() {
final double EXPECTED = 4;
final double ACTUAL = Calculator.divide(8.0,2.0);
assertEquals(EXPECTED,ACTUAL);
}
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Okey, we see the assert word, but what is that?
Assertions
Assertion is a statement in java. It can be used to test your assumptions about the program.
JUnit 5 assertions help in validating the expected output with actual output of a testcase. To keep things simple, all JUnit Jupiter assertions are static methods in the org.junit.jupiter.Assertions class. List of every possible assertions is here: https://junit.org/junit5/docs/5.7.2/api/org.junit.jupiter.api/org/junit/jupiter/api/Assertions.html