-
Notifications
You must be signed in to change notification settings - Fork 3.2k
Getting started
This small example shows you how to write a unit test. You need to have a JDK installed and a text editor. (In general it is recommended to use a build tool for building your software and running the tests.)
Create a new folder junit-example
and download the current junit-4.XX.jar
from JUnit's release page and Hamcrest to this folder. Change to the folder junit-example
. All files are created within this folder and all commands are executed there, too.
Create a new file Calculator.java
and copy the following code to this file.
public class Calculator {
public int evaluate(String expression) {
int sum = 0;
for (String summand: expression.split("\\ "))
sum = Integer.valueOf(summand);
return sum;
}
}
Now compile this class:
javac Calculator.java
The Java compiler creates a file Calculator.class
.
Create the file CalculatorTest.java
and copy the following code to this file.
import static org.junit.Assert.assertEquals;
import org.junit.Test;
public class CalculatorTest {
@Test
public void evaluatesExpression() {
Calculator calculator = new Calculator();
int sum = calculator.evaluate("1 2 3");
assertEquals(6, sum);
}
}
Compile the test. On Linux or MacOS
javac -cp .:junit-4.XX.jar:hamcrest-core-1.3.jar CalculatorTest.java
and on Windows
javac -cp .;junit-4.XX.jar;hamcrest-core-1.3.jar CalculatorTest.java
The Java compiler creates a file CalculatorTest.class
.
Run the test from the command line. On Linux or MacOS
java -cp .:junit-4.XX.jar:hamcrest-core-1.3.jar org.junit.runner.JUnitCore CalculatorTest
and on Windows
java -cp .;junit-4.XX.jar;hamcrest-core-1.3.jar org.junit.runner.JUnitCore CalculatorTest
The output is
JUnit version 4.12
.
Time: 0,006
OK (1 test)
The single .
means that one test has been run and the OK
in the last line tells you that your test is successful.
Modify Calculator.java
in order to get a failing test. Replace the line
sum = Integer.valueOf(summand);
with
sum -= Integer.valueOf(summand);
and recompile the class.
javac Calculator.java
Run the test again. On Linux or MacOS
java -cp .:junit-4.XX.jar:hamcrest-core-1.3.jar org.junit.runner.JUnitCore CalculatorTest
and on Windows
java -cp .;junit-4.XX.jar;hamcrest-core-1.3.jar org.junit.runner.JUnitCore CalculatorTest
Now the test fails and the output is
JUnit version 4.12
.E
Time: 0,007
There was 1 failure:
1) evaluatesExpression(CalculatorTest)
java.lang.AssertionError: expected:<6> but was:<-6>
at org.junit.Assert.fail(Assert.java:88)
...
FAILURES!!!
Tests run: 1, Failures: 1
JUnit tells you which test failed (evaluatesExpression(CalculatorTest)
) and what went wrong:
java.lang.AssertionError: expected:<6> but was:<-6>