Exercises: Unit Testing
Work on these exercises in the IntelliJ car-exercises
project in java-web-dev-projects/unit-testing/exercises
. You will update your CarTest.java
file by adding
more test cases.
testGasTankAfterDriving()
Add a test for the third TODO, “gasTankLevel is accurate after driving within tank range”.
Your test must use the
Car
methoddrive()
test_car.drive(50);
With a value of
50
miles passed intodrive()
, we expecttest_car
to have agasTankLevel
of9
.assertEquals(9, test_car.getGasTankLevel(), .001);
testGasTankAfterExceedingTankRange()
Add a test for the fourth TODO, “gasTankLevel is accurate after attempting to drive past tank range”.
- You’re on your own for this one. You’ll need to simulate the
Car
traveling farther than it’sgasTankLevel
allows.
testGasOverfillException()
The test for our last TODO is a little different. We are going to perform an action on our car object, and we are expecting the object to throw an error. In this case, we are going to attempt to add gas to our car that exceeds the gas tank size.
First, we’ll add some code to our test to tell JUnit to expect an exception.
//TODO: can't have more gas than tank size, expect an exception @Test() public void testGasOverfillException() { assertThrows(IllegalArgumentException.class, () -> ); }
This lets JUnit know that this test should pass if an
IllegalArgumentException
is thrown at any point during this test.Update the
Car
class to include anaddGas()
method.public void addGas(double gas) { this.setGasTankLevel(gas + this.getGasTankLevel()); }
Back in
CarTest
, implement the newaddGas()
method and what should happen if the exception is thrown after the->
syntax using this code:test_car.addGas(5), "Shouldn't get here, car cannot have more gas in tank than the size of the tank"
. The string will be displayed if the test fails.Run the test. It should fail! In the output is an unexpected exception. This test was expecting an
IllegalArgumentException
, but it got anAssertionError
exception. This caused the test to fail.We need to refactor
Car
to throw an exception when too much gas is added to the tank. Find thesetGasTankLevel
method and modify it:public void setGasTankLevel(double gasTankLevel) { if (gasTankLevel > this.getGasTankSize()) { throw new IllegalArgumentException("Can't exceed tank size"); } this.gasTankLevel = gasTankLevel; }
Now, run the test - it should pass!