In this tutorial we will dive into JUnit5 framework even more basing on very simple Calculator project.
The tutorial repository can be found here:
Project Structure:
.
├── pom.xml
└── src
├── main
│ └── java
│ └── Calculator.java
└── test
└── java
└── CalculatorTest.java
Our Calculator.java look like this:
As you can see it has only divide() method, that checks if b is equal to 0. If it is, it throws an exception.
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());
}
}
So let's write first simple test, but before that we need to know what the assertion are.
1. 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. (The order is always the same!!)
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
So our test class looks like this:
@Test
@DisplayName("Divide two finite numbers")
void divideTest() {
final double EXPECTED = 4;
final double ACTUAL = Calculator.divide(8.0,2.0);
assertEquals(EXPECTED,ACTUAL);
}
2. Exceptions
To ensure our error handling works correctly, we can verify that a piece of code throws a specific exception under certain conditions.
This can be done with the assertThrows() method in JUnit 5: If we catch this thrown exception test is passed.
@Test
@DisplayName("Divide by 0")
void divideBy0ExpectedExceptionTest() {
assertThrows(ArithmeticException.class, () -> {
Calculator.divide(8.0,0.0);
});