Using JUnit5 – Part 2 – Testing Basics

java, junit5

Published: 2019-07 (July 2019)
Relevant for: JUnit 5.5.0

JUnit5 Blog Series

Part 1 – Introduction
Part 2 – Test Basics
Part 3 – Display Names
Part 4 – Filtering tests

In Part 1 of the blog series, we looked at several annotations used in JUnit5. We covered test methods as well as lifecycle methods.

This post will share examples of a JUnit test which has a few of these annotations.

We will use a recently created code kata for the examples.

Testing

Marking a method as a Test

Tests in JUnit5 are annotated with the @Test annotation. Unlike prior versions of JUnit, the JUnit5 @Test annotation does not have any attributes. Prior versions supported extensions via attributes, while JUnit5 fosters a custom annotation based extension (more on this in a future blog).

Example: @Test (https://github.com/c-guntur/java-katas/blob/baseline/java-datetime/src/solutions/java/none/cvg/datetime/STest1InstantAndDateInteropTest.java#L43)

    @Test
    @Tag("PASSING")
    @Order(1)
    public void verifyInstantAndDateHaveSameEpochMilliseconds() {

        // DONE: Replace the Instant.now() with an instant from classicDate.
        //  Use a Date API that converts Date instances into Instant instances.
        //  Check: java.util.Date.toInstant()
        Instant instant = classicDate.toInstant();

        // DONE: Replace the "null" below to get milliseconds from epoch from the Instant
        //  Use an Instant API which converts it into milliseconds
        //  Check: java.time.Instant.toEpochMilli()
        assertEquals(Long.valueOf(classicDate.getTime()),
                instant.toEpochMilli(),
                "Date and Instant milliseconds should be equal");
    }

Assertions

Assertions are how testing is conducted. Several types of assertions exist for testing. Some examples include:

  • assertTrue / assertFalse
  • assertEquals / assertNotEquals / assertSame / assertNotSame
  • assertNull / assertNotNull
  • assertArrayEquals / assertIterableEquals / assertLinesMatch
  • assertThrows / assertNotThrows
  • assertAll
  • assertTimeout / assertTimeoutPreemptively
  • fail

There are several polymorphs for most of the methods listed above. JUnit5 aggregates all such assertions as static methods in a single factory utility aptly named Assertions (https://junit.org/junit5/docs/5.5.0/api/org/junit/jupiter/api/Assertions.html).

Assertions are mostly unary or binary (There are assertions, with other arities, that are less commonly used)

Unary assertions are usually boolean condition evaluators. assertTrue or assertNull are good examples of unary assertions. The expectation in such cases is built into the actual assertion method name. A second optional parameter for unary assertions is a message that is returned in case of an assertion failure and exists to provide more meaningful readable failure details.

Binary assertions typically have an expected value (a known), an actual value (evaluated) and an optional third parameter of message (in case of the expectation not being met). assertEquals and assertSame are good examples of binary assertions.

Typically, unit tests statically import the assertions required for the given tests in a test class. An example of such an assertion is the assertEquals method as shown below.

Example: Assertion (https://github.com/c-guntur/java-katas/blob/baseline/java-datetime/src/solutions/java/none/cvg/datetime/STest1InstantAndDateInteropTest.java#L56)

    @Test
    @Tag("PASSING")
    @Order(1)
    public void verifyInstantAndDateHaveSameEpochMilliseconds() {

        // DONE: Replace the Instant.now() with an instant from classicDate.
        //  Use a Date API that converts Date instances into Instant instances.
        //  Check: java.util.Date.toInstant()
        Instant instant = classicDate.toInstant();

        // DONE: Replace the "null" below to get milliseconds from epoch from the Instant
        //  Use an Instant API which converts it into milliseconds
        //  Check: java.time.Instant.toEpochMilli()
        assertEquals(Long.valueOf(classicDate.getTime()),
                instant.toEpochMilli(),
                "Date and Instant milliseconds should be equal");
    }

See also: Static Import (https://github.com/c-guntur/java-katas/blob/baseline/java-datetime/src/solutions/java/none/cvg/datetime/STest1InstantAndDateInteropTest.java#L18)

import java.text.SimpleDateFormat;
import java.time.Instant;
import java.util.Date;
import java.util.TimeZone;

import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.DisplayNameGeneration;
import org.junit.jupiter.api.MethodOrderer;
import org.junit.jupiter.api.Order;
import org.junit.jupiter.api.Tag;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.TestMethodOrder;

import static none.cvg.datetime.LenientAssert.assertAlmostEquals;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertTrue;

NOTE: Assertion parameter ordering in JUnit 5 is different from the order in prior versions. In my opinion, the current parameter arrangement makes a lot more sense.

Filtering and Categorizing Tests

Tags

Tags are a means to categorize test methods and classes. Tagging also leads to discovery and filtering of tests. Tagging is done by annotating the class or method with an @Tag annotation. More on filtering in another blog of this series.

Example: @Tag (https://github.com/c-guntur/java-katas/blob/baseline/java-datetime/src/solutions/java/none/cvg/datetime/STest1InstantAndDateInteropTest.java#L62)

    @Test
    @Tag("PASSING")
    @Order(1)
    public void verifyInstantAndDateHaveSameEpochMilliseconds() {

        // DONE: Replace the Instant.now() with an instant from classicDate.
        //  Use a Date API that converts Date instances into Instant instances.
        //  Check: java.util.Date.toInstant()
        Instant instant = classicDate.toInstant();

        // DONE: Replace the "null" below to get milliseconds from epoch from the Instant
        //  Use an Instant API which converts it into milliseconds
        //  Check: java.time.Instant.toEpochMilli()
        assertEquals(Long.valueOf(classicDate.getTime()),
                instant.toEpochMilli(),
                "Date and Instant milliseconds should be equal");
    }

Assumptions

Assumptions are conditions that determine if the rest of the test code block should be either evaluated or aborted. Not meeting an assumption will not cause the code block conditioned by it, to fail. It would rather simply abort execution of such a code block. Some assumption methods:

  • assumeTrue / assumeFalse
  • assumeThat

Similar to assertions, assumptions are grouped as static methods, in a factory utility class, Assumptions (https://junit.org/junit5/docs/5.5.0/user-guide/#writing-tests-assumptions).

class TestWithAssumptions {

    @Test
    void testOnlyOnHost123() {
        assumeTrue("host123".equals(System.getenv("HOSTNAME")));
        // remainder of test
    }

    @Test
    void testOnHost123OrAbortWithMessage() {
        assumeTrue("host123".equals(System.getenv("HOSTNAME")),
            () -> "Aborting test: not on host123");
        // remainder of test
    }

}

Typically, unit tests statically import the assumptions required for the given tests in a test class.

There is no current example of an assumption in the code kata.

Ordering Tests

Test execution order

As stated in the previous part of the blog series, I reserve my opinions of ordering the sequence of test executions. It is useful in certain cases, such as code katas. Test ordering requires either one or two steps depending on the type of ordering.

NOTE: If no order is specified for a test class, JUnit 5 looks for instructions from parent class hierarchy and if still none found, will order tests in a deterministic but non-obvious manner.

Instructing JUnit to order tests

An annotation on the test class is needed to instruct JUnit5 to order tests. This annotation is called the @TestMethodOrder. This annotation accepts an attribute of type MethodOrderer. There are three default implementations that exist:

  1. Alphanumeric – uses String::compareTo to order execution of test methods
  2. OrderAnnotation – uses the @Order annotation on each test method to determine order. The Order annotation accepts a int attribute that specifies the ranking.
  3. Random – uses a random order either simply from System.nanoTime() or in combination with a custom seed.

More custom orders can be created by implementing the MethodOrderer interface.

Example: @TestMethodOrder (https://github.com/c-guntur/java-katas/blob/baseline/java-datetime/src/solutions/java/none/cvg/datetime/STest1InstantAndDateInteropTest.java#L31)

/**
 * The tests in this class aim to show interoperability between
 * `java.util.Date` and the newer `java.time.Instant`.
 *
 * @see Instant
 * @see Date
 * @see LenientAssert
 */
@DisplayNameGeneration(DateTimeKataDisplayNames.class)
@DisplayName("Instant And Date Interoperability")
@TestMethodOrder(MethodOrderer.OrderAnnotation.class)
public class STest1InstantAndDateInteropTest {

Extra Step (For OrderAnnotation only): Adding an Order via annotations

In addition to the above annotation instructing JUnit to order test methods, an additional annotation is needed if the OrderAnnotation orderer is specified. The @Order annotation accepts an integer that specifies the ascending order of execution.

Example: @Order (https://github.com/c-guntur/java-katas/blob/baseline/java-datetime/src/solutions/java/none/cvg/datetime/STest1InstantAndDateInteropTest.java#L45)

    @Test
    @Tag("PASSING")
    @Order(1)
    public void verifyInstantAndDateHaveSameEpochMilliseconds() {

        // DONE: Replace the Instant.now() with an instant from classicDate.
        //  Use a Date API that converts Date instances into Instant instances.
        //  Check: java.util.Date.toInstant()
        Instant instant = classicDate.toInstant();

        // DONE: Replace the "null" below to get milliseconds from epoch from the Instant
        //  Use an Instant API which converts it into milliseconds
        //  Check: java.time.Instant.toEpochMilli()
        assertEquals(Long.valueOf(classicDate.getTime()),
                instant.toEpochMilli(),
                "Date and Instant milliseconds should be equal");
    }

That’s a wrap of part two of this blog series. The next blog will include customizing tests with DisplayNames and writing a custom DisplayNameGeneration. Happy coding !

Part 1 – Introduction
Part 2 – Test Basics
Part 3 – Display Names
Part 4 – Filtering tests

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