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Java Unit Testing in Java What to Test Know Your Bounds

Posted by Mohamed Tawfik
Mohamed Tawfik
Courses Plus Student 19,338 Points

Handling exceptions in JUnit 5

I can't handle exceptions in JUnit 5 Neither by the Expected keyword nor by the Rule annotation

Kjetil Lorentzen
Kjetil Lorentzen
13,360 Points
Kjetil Lorentzen
Kjetil Lorentzen
13,360 Points

Hi Mohamed,

I got into the same problem you were experiencing after watching the videos and using JUnit5. After some googling I found that there is a new (and perhaps improved) way of doing unit testing when testing for expected messages from thrown exceptions.

See below for my implementation:

private Throwable thrown;

@Test
    void overstockingNotAllowed() {
        thrown = assertThrows(IllegalArgumentException.class, () -> {
            bin.restock("Fritos", 2600, 100, 50);
        });
        assertEquals("There are only 10 spots left", thrown.getMessage());
    }
'''

4 Answers

Miguel Nunez
Miguel Nunez
1,081 Points
Miguel Nunez
Miguel Nunez
1,081 Points 
@Test
    void overStockingNotAllowed() {

        assertThrows(IllegalArgumentException.class, () ->
                        bin.restock("Mars", 15, 100, 50),
                "There are only 10 spots left");
Daniel Marin
Daniel Marin
8,021 Points
Daniel Marin
Daniel Marin
8,021 Points

I'm using junit5 as well here's an example for the vending project:

    @Test
    void notEnoughFundsToDeduct() {
        Assertions.assertThrows(NotEnoughFundsException.class, () -> creditor.deduct(10));
    }
Oziel Perez
Oziel Perez
61,321 Points
Oziel Perez
Oziel Perez
61,321 Points

Per the docs:

@Test
void exceptionTesting() {
    Throwable exception = assertThrows(IllegalArgumentException.class, () -> {
        throw new IllegalArgumentException("a message");
    });
    assertEquals("a message", exception.getMessage());
}

@Rule no longer exists in JUnit 5 and is superseded by @ExtendedWith. However, there is a migration guide which helps continue to use the @Rule annotation, but this is recommended only to those that have large fixtures with multiple rules and don't wish to rewrite all their tests right away.

Muhammad Nagy
Muhammad Nagy
944 Points
Muhammad Nagy
Muhammad Nagy
944 Points

In JUnit 5, the test should be rewritten like the following

  @Test
  void overstockingNotAllowed() {
    IllegalArgumentException thrown =
        assertThrows(
            IllegalArgumentException.class,
            () -> {
              bin.restock("Fritos", 2600, 100, 50);
            });
    assertTrue(thrown.getMessage().equals("There are only 10 spots left"));
  }