Pernyataan di JUnit 4 dan JUnit 5

1. Perkenalan

Pada artikel ini, kami akan menjelajahi secara detail pernyataan yang tersedia dalam JUnit.

Setelah artikel migrasi dari JUnit 4 ke JUnit 5 dan A Guide ke JUnit 5, sekarang kita akan membahas detail tentang pernyataan berbeda yang tersedia di JUnit 4 dan JUnit 5.

Kami juga akan menyoroti peningkatan yang dibuat pada pernyataan dengan JUnit 5.

2. Pernyataan

Pernyataan adalah metode utilitas untuk mendukung penetapan kondisi dalam pengujian ; metode ini dapat diakses melalui kelas Assert , di JUnit 4, dan Assertions satu, di JUnit 5.

Untuk meningkatkan keterbacaan pengujian dan pernyataan itu sendiri, selalu disarankan untuk mengimpor kelas terkait secara statis. Dengan cara ini, kita bisa merujuk langsung ke metode pernyataan itu sendiri tanpa kelas yang mewakili sebagai awalan.

Mari kita mulai menjelajahi pernyataan yang tersedia dengan JUnit 4.

3. Pernyataan di JUnit 4

Dalam versi pustaka ini, pernyataan tersedia untuk semua tipe primitif, Objek, dan larik (baik primitif atau Objek).

Urutan parameter, dalam pernyataan, adalah nilai yang diharapkan diikuti dengan nilai aktual; opsional, parameter pertama dapat berupa pesan String yang mewakili output pesan dari kondisi yang dievaluasi.

Hanya ada satu perbedaan kecil dalam cara mendefinisikan assertThat assertions, tetapi kami akan membahasnya nanti.

Mari kita mulai dengan assertEquals .

3.1. assertEquals

The assertEquals memverifikasi pernyataan bahwa diharapkan dan nilai-nilai yang sebenarnya adalah sama:

@Test public void whenAssertingEquality_thenEqual() { String expected = "Baeldung"; String actual = "Baeldung"; assertEquals(expected, actual); }

Ini juga memungkinkan untuk menentukan pesan untuk ditampilkan ketika pernyataan gagal:

assertEquals("failure - strings are not equal", expected, actual);

3.2. assertArrayEquals

Jika kita ingin menyatakan bahwa dua array sama, kita dapat menggunakan assertArrayEquals:

@Test public void whenAssertingArraysEquality_thenEqual() { char[] expected = {'J','u','n','i','t'}; char[] actual = "Junit".toCharArray(); assertArrayEquals(expected, actual); }

Jika kedua larik bernilai nol , pernyataan akan menganggapnya sama:

@Test public void givenNullArrays_whenAssertingArraysEquality_thenEqual() { int[] expected = null; int[] actual = null; assertArrayEquals(expected, actual); }

3.3. assertNotNull dan assertNull

Saat kami ingin menguji apakah suatu objek bernilai null, kami dapat menggunakan pernyataan assertNull :

@Test public void whenAssertingNull_thenTrue() { Object car = null; assertNull("The car should be null", car); }

Sebaliknya, jika kita ingin menyatakan bahwa suatu objek tidak boleh null, kita dapat menggunakan assertion assertNotNull.

3.4. assertNotSame dan assertSame

Dengan assertNotSame , dimungkinkan untuk memverifikasi jika dua variabel tidak merujuk ke objek yang sama:

@Test public void whenAssertingNotSameObject_thenDifferent() { Object cat = new Object(); Object dog = new Object(); assertNotSame(cat, dog); }

Jika tidak, saat kita ingin memverifikasi bahwa dua variabel merujuk ke objek yang sama, kita dapat menggunakan pernyataan assertSame .

3.5. assertTrue dan assertFalse

Jika kita ingin memverifikasi bahwa kondisi tertentu benar atau salah , kita masing-masing dapat menggunakan assertTrue assertion atau assertFalse :

@Test public void whenAssertingConditions_thenVerified() { assertTrue("5 is greater then 4", 5 > 4); assertFalse("5 is not greater then 6", 5 > 6); }

3.6. gagal

The gagal pernyataan gagal tes melempar AssertionFailedError . Ini dapat digunakan untuk memverifikasi bahwa pengecualian aktual dilemparkan atau ketika kami ingin membuat pengujian gagal selama pengembangannya.

Mari kita lihat bagaimana kita bisa menggunakannya di skenario pertama:

@Test public void whenCheckingExceptionMessage_thenEqual() { try { methodThatShouldThrowException(); fail("Exception not thrown"); } catch (UnsupportedOperationException e) { assertEquals("Operation Not Supported", e.getMessage()); } }

3.7. assertThat

The assertThat penegasan adalah satu-satunya di JUnit 4 yang memiliki urutan terbalik dari parameter dibandingkan dengan pernyataan lainnya.

Dalam kasus ini, pernyataan memiliki pesan kegagalan opsional, nilai sebenarnya, dan objek Matcher .

Mari kita lihat bagaimana kita bisa menggunakan pernyataan ini untuk memeriksa apakah sebuah array berisi nilai tertentu:

@Test public void testAssertThatHasItems() { assertThat( Arrays.asList("Java", "Kotlin", "Scala"), hasItems("Java", "Kotlin")); } 

Informasi tambahan, tentang penggunaan yang kuat dari pernyataan assertThat dengan objek Matcher , tersedia di Menguji dengan Hamcrest.

4. JUnit 5 Assertions

JUnit 5 menyimpan banyak metode pernyataan JUnit 4 sambil menambahkan beberapa metode baru yang memanfaatkan dukungan Java 8.

Juga dalam versi pustaka ini, pernyataan tersedia untuk semua tipe primitif, Objek, dan larik (baik primitif atau Objek).

The order of the parameters of the assertions changed, moving the output message parameter as the last parameter. Thanks to the support of Java 8, the output message can be a Supplier, allowing lazy evaluation of it.

Let's start reviewing the assertions available also in JUnit 4.

4.1. assertArrayEquals

The assertArrayEquals assertion verifies that the expected and the actual arrays are equals:

@Test public void whenAssertingArraysEquality_thenEqual() { char[] expected = { 'J', 'u', 'p', 'i', 't', 'e', 'r' }; char[] actual = "Jupiter".toCharArray(); assertArrayEquals(expected, actual, "Arrays should be equal"); }

If the arrays aren't equal, the message “Arrays should be equal” will be displayed as output.

4.2. assertEquals

In case we want to assert that two floats are equals, we can use the simple assertEquals assertion:

@Test public void whenAssertingEquality_thenEqual() { float square = 2 * 2; float rectangle = 2 * 2; assertEquals(square, rectangle); }

However, if we want to assert that the actual value differs by a predefined delta from the expected value, we can still use the assertEquals but we have to pass the delta value as the third parameter:

@Test public void whenAssertingEqualityWithDelta_thenEqual() { float square = 2 * 2; float rectangle = 3 * 2; float delta = 2; assertEquals(square, rectangle, delta); }

4.3. assertTrue and assertFalse

With the assertTrue assertion, it's possible to verify the supplied conditions are true:

@Test public void whenAssertingConditions_thenVerified() { assertTrue(5 > 4, "5 is greater the 4"); assertTrue(null == null, "null is equal to null"); }

Thanks to the support of the lambda expression, it's possible to supply a BooleanSupplier to the assertion instead of a boolean condition.

Let's see how we can assert the correctness of a BooleanSupplier using the assertFalse assertion:

@Test public void givenBooleanSupplier_whenAssertingCondition_thenVerified() { BooleanSupplier condition = () -> 5 > 6; assertFalse(condition, "5 is not greater then 6"); }

4.4. assertNull and assertNotNull

When we want to assert that an object is not null we can use the assertNotNull assertion:

@Test public void whenAssertingNotNull_thenTrue() { Object dog = new Object(); assertNotNull(dog, () -> "The dog should not be null"); }

In the opposite way, we can use the assertNull assertion to check if the actual is null:

@Test public void whenAssertingNull_thenTrue() { Object cat = null; assertNull(cat, () -> "The cat should be null"); }

In both cases, the failure message will be retrieved in a lazy way since it's a Supplier.

4.5. assertSame and assertNotSame

When we want to assert that the expected and the actual refer to the same Object, we must use the assertSame assertion:

@Test public void whenAssertingSameObject_thenSuccessfull() { String language = "Java"; Optional optional = Optional.of(language); assertSame(language, optional.get()); }

In the opposite way, we can use the assertNotSame one.

4.6. fail

The fail assertion fails a test with the provided failure message as well as the underlying cause. This can be useful to mark a test when it's development it's not completed:

@Test public void whenFailingATest_thenFailed() { // Test not completed fail("FAIL - test not completed"); }

4.7. assertAll

One of the new assertion introduced in JUnit 5 is assertAll.

This assertion allows the creation of grouped assertions, where all the assertions are executed and their failures are reported together. In details, this assertion accepts a heading, that will be included in the message string for the MultipleFailureError, and a Stream of Executable.

Let's define a grouped assertion:

@Test public void givenMultipleAssertion_whenAssertingAll_thenOK() { assertAll( "heading", () -> assertEquals(4, 2 * 2, "4 is 2 times 2"), () -> assertEquals("java", "JAVA".toLowerCase()), () -> assertEquals(null, null, "null is equal to null") ); }

The execution of a grouped assertion is interrupted only when one of the executables throws a blacklisted exception (OutOfMemoryError for example).

4.8. assertIterableEquals

The assertIterableEquals asserts that the expected and the actual iterables are deeply equal.

In order to be equal, both iterable must return equal elements in the same order and it isn't required that the two iterables are of the same type in order to be equal.

With this consideration, let's see how we can assert that two lists of different types (LinkedList and ArrayList for example) are equal:

@Test public void givenTwoLists_whenAssertingIterables_thenEquals() { Iterable al = new ArrayList(asList("Java", "Junit", "Test")); Iterable ll = new LinkedList(asList("Java", "Junit", "Test")); assertIterableEquals(al, ll); }

In the same way of the assertArrayEquals, if both iterables are null, they are considered equal.

4.9. assertLinesMatch

The assertLinesMatch asserts that the expected list of String matches the actual list.

This method differs from the assertEquals and assertIterableEquals since, for each pair of expected and actual lines, it performs this algorithm:

  1. check if the expected line is equal to the actual one. If yes it continues with the next pair
  2. treat the expected line as a regular expression and performs a check with the String.matches() method. If yes it continues with the next pair
  3. check if the expected line is a fast-forward marker. If yes apply fast-forward and repeat the algorithm from the step 1

Let's see how we can use this assertion to assert that two lists of String have matching lines:

@Test public void whenAssertingEqualityListOfStrings_thenEqual() { List expected = asList("Java", "\\d+", "JUnit"); List actual = asList("Java", "11", "JUnit"); assertLinesMatch(expected, actual); }

4.10. assertNotEquals

Complementary to the assertEquals, the assertNotEquals assertion asserts that the expected and the actual values aren't equal:

@Test public void whenAssertingEquality_thenNotEqual() { Integer value = 5; // result of an algorithm assertNotEquals(0, value, "The result cannot be 0"); }

If both are null, the assertion fails.

4.11. assertThrows

In order to increase simplicity and readability, the new assertThrows assertion allows us a clear and a simple way to assert if an executable throws the specified exception type.

Let's see how we can assert a thrown exception:

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

The assertion will fail if no exception is thrown, or if an exception of a different type is thrown.

4.12. assertTimeout and assertTimeoutPreemptively

In case we want to assert that the execution of a supplied Executable ends before a given Timeout, we can use the assertTimeout assertion:

@Test public void whenAssertingTimeout_thenNotExceeded() { assertTimeout( ofSeconds(2), () -> { // code that requires less then 2 minutes to execute Thread.sleep(1000); } ); }

However, with the assertTimeout assertion, the supplied executable will be executed in the same thread of the calling code. Consequently, execution of the supplier won't be preemptively aborted if the timeout is exceeded.

In case we want to be sure that execution of the executable will be aborted once it exceeds the timeout, we can use the assertTimeoutPreemptively assertion.

Kedua pernyataan tersebut dapat menerima, alih-alih Executable, sebuah ThrowingSupplier , yang merepresentasikan blok kode generik apa pun yang mengembalikan sebuah objek dan yang berpotensi memunculkan Throwable.

5. Kesimpulan

Dalam tutorial ini, kami membahas semua pernyataan yang tersedia di JUnit 4 dan JUnit 5.

Kami menyoroti secara singkat peningkatan yang dibuat di JUnit 5, dengan pengenalan pernyataan baru dan dukungan lambda.

Seperti biasa, kode sumber lengkap untuk artikel ini tersedia di GitHub.