Selecting tests by tags and classes in JUnit - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of JUnit test run with tag filter

Given the following JUnit 5 test classes with tags, what will be the output when running tests with the tag @Tag("fast") only?

JUnit

import org.junit.jupiter.api.Tag;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertTrue;

public class FastTests {
    @Test
    @Tag("fast")
    void fastTest1() {
        assertTrue(true);
    }

    @Test
    @Tag("slow")
    void slowTest1() {
        assertTrue(true);
    }
}

public class MixedTests {
    @Test
    @Tag("fast")
    void fastTest2() {
        assertTrue(true);
    }

    @Test
    void noTagTest() {
        assertTrue(true);
    }
}

A Only slowTest1 runs because it has a tag; others are skipped.

B All tests run regardless of tags and all pass.

C Only tests without tags run; fastTest1, fastTest2, and slowTest1 are skipped.

D Only fastTest1 and fastTest2 run and pass; slowTest1 and noTagTest are skipped.

💡 Hint

Remember that JUnit 5 allows filtering tests by tags using the @Tag annotation and test runners can include or exclude tests by tag.

When running tests filtered by the tag "fast", only tests annotated with @Tag("fast") will run. Tests with other tags or no tags are skipped.

❓ assertion

intermediate

Correct assertion to verify only tagged tests ran

You run JUnit tests filtered by tag "integration". Which assertion correctly verifies that only tests with this tag ran?

JUnit

import org.junit.jupiter.api.Tag;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertEquals;

// Assume testResults is a list of test names that ran
List<String> testResults = List.of("integrationTest1", "integrationTest2");

A assertEquals(2, testResults.size());

B assertEquals(4, testResults.size());

C assertEquals(0, testResults.size());

D assertEquals(1, testResults.size());

💡 Hint

Count how many tests have the "integration" tag and expect only those to run.

If only tests tagged "integration" run, and there are exactly two such tests, the size of testResults should be 2.

🔧 Debug

advanced

Why does filtering by tag fail to exclude untagged tests?

You configured your JUnit 5 test run to include only tests with tag "ui" but untagged tests still run. What is the most likely cause?

A The test runner configuration is missing the tag filter include directive.

B Tests without tags are always included by default and cannot be excluded.

C JUnit 5 does not support filtering by tags.

D The @Tag annotation is only for documentation and does not affect test execution.

💡 Hint

Check your test runner or build tool configuration for tag filtering settings.

JUnit 5 supports tag filtering, but the runner must be explicitly configured to include or exclude tags. Without this, all tests run.

❓ framework

advanced

Selecting tests by class and tag in JUnit 5

Which JUnit 5 command line option runs only tests in class LoginTests tagged with smoke?

A junit-platform-console --select-package=LoginTests --include-tags=smoke

B junit-platform-console --select-package=LoginTests --exclude-tags=smoke

C junit-platform-console --select-class=LoginTests --include-tags=smoke

D junit-platform-console --select-class=LoginTests --exclude-tags=smoke

💡 Hint

Use --select-class to specify the test class and --include-tags to filter by tag.

The option --select-class=LoginTests selects that class, and --include-tags=smoke filters tests to only those tagged "smoke".

🧠 Conceptual

expert

Impact of multiple tags on test selection

If a test method is annotated with @Tag("fast") and @Tag("database"), and the test run includes only tests tagged "fast", what happens?

A The test is excluded because it has more than one tag.

B The test runs because it has the "fast" tag, even though it also has "database".

C The test runs only if both tags are included in the filter.

D The test is excluded because it has the "database" tag.

💡 Hint

Think about how tag filters include tests that have at least one matching tag.

JUnit 5 includes tests that have any of the included tags. Having multiple tags does not exclude a test if one tag matches the filter.