@EnabledOnJre for JRE-specific tests in JUnit - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a test annotated with @EnabledOnJre for Java 17

Consider this JUnit 5 test class snippet. What will be the test execution result if run on Java 17?

JUnit

import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.condition.EnabledOnJre;
import org.junit.jupiter.api.condition.JRE;

public class SampleTest {

    @Test
    @EnabledOnJre(JRE.JAVA_17)
    void testOnlyOnJava17() {
        System.out.println("Running on Java 17");
    }

    @Test
    void alwaysRun() {
        System.out.println("Always runs");
    }
}

A Both tests run and print their messages.

B Only the test annotated with @EnabledOnJre runs and prints its message.

C Only the test without @EnabledOnJre runs and prints its message.

D Neither test runs because @EnabledOnJre disables all tests.

💡 Hint

Think about what @EnabledOnJre does and which tests have it.

The test annotated with @EnabledOnJre(JRE.JAVA_17) runs only on Java 17. The other test runs always. So on Java 17 both run.

❓ assertion

intermediate

Correct assertion to verify @EnabledOnJre disables test on Java 11

You want to assert that a test annotated with @EnabledOnJre(JRE.JAVA_17) does NOT run on Java 11. Which assertion correctly verifies this behavior in a test suite?

A assertFalse(testExecuted, "Test should not run on Java 11");

B assertTrue(testExecuted, "Test should run on Java 11");

C assertEquals("Running", testOutput);

D assertNull(testExecuted);

💡 Hint

If the test is disabled, it should not have executed.

On Java 11, the test with @EnabledOnJre(JRE.JAVA_17) is disabled, so testExecuted should be false.

🔧 Debug

advanced

Why does @EnabledOnJre not disable test on Java 18?

Given this test annotation: @EnabledOnJre(JRE.JAVA_17), why does the test still run on Java 18?

A Because the annotation is ignored on Java versions higher than 17.

B Because @EnabledOnJre matches the specified JRE and all later versions, so Java 18 is included and test runs.

C Because @EnabledOnJre matches only the exact JRE version specified, so Java 18 is not matched and test is disabled.

D Because @EnabledOnJre only disables tests on earlier versions, not later ones.

💡 Hint

Check how @EnabledOnJre matches JRE versions exactly.

The annotation matches only the exact JRE version specified. Java 18 is different from Java 17, so the test is disabled on Java 18.

🧠 Conceptual

advanced

Purpose of @EnabledOnJre in test suites

What is the main purpose of using @EnabledOnJre in JUnit test suites?

A To automatically upgrade Java version before running tests.

B To disable tests permanently regardless of Java version.

C To run tests only on operating systems matching the JRE version.

D To run tests only on specific Java Runtime Environment versions.

💡 Hint

Think about controlling test execution based on Java version.

The annotation controls test execution so tests run only on specified Java versions.

❓ framework

expert

Combining @EnabledOnJre with other conditional annotations

You want a test to run only on Java 17 and only on Windows OS. Which annotation combination correctly achieves this in JUnit 5?

A @EnabledOnJre(JRE.JAVA_17, OS.WINDOWS)

B @EnabledOnJre(JRE.JAVA_17) @EnabledOnOs(OS.WINDOWS)

C @EnabledOnOs(OS.WINDOWS) @EnabledOnJre(OS.WINDOWS, JRE.JAVA_17)

D @EnabledOnJre(OS.WINDOWS) @EnabledOnOs(JRE.JAVA_17)

💡 Hint

Use separate annotations for JRE and OS conditions.

JUnit 5 requires separate annotations for JRE and OS conditions. Option B correctly uses @EnabledOnJre and @EnabledOnOs separately.

Practice

1. What is the main purpose of the @EnabledOnJre annotation in JUnit?

easy

A. To run a test only on specified Java Runtime Environment versions

B. To disable a test permanently

C. To run a test on all Java versions except specified ones

D. To enable tests only on the latest Java version

Solution

1. Step 1: Understand the annotation purpose

   <code>@EnabledOnJre

2. Step 2: Match purpose with options

   To run a test only on specified Java Runtime Environment versions correctly states it runs tests only on specified JRE versions, while others describe different behaviors.

3. Final Answer:

   To run a test only on specified Java Runtime Environment versions -> Option A

4. Quick Check:

   @EnabledOnJre = run test on chosen JRE versions [OK]

Hint: Think: runs tests only on chosen Java versions [OK]

Common Mistakes:

• Confusing @EnabledOnJre with disabling tests
• Assuming it runs tests on all versions except specified
• Thinking it only enables tests on the latest Java version

2. Which of the following is the correct syntax to enable a test only on Java 17 using @EnabledOnJre?

easy

A. @EnabledOnJre(javaVersion = "17")

B. @EnabledOnJre(version = 17)

C. @EnabledOnJre(JRE.JAVA_17)

D. @EnabledOnJre(value = "JAVA_17")

Solution

1. Step 1: Recall correct annotation usage

   The correct syntax uses the enum constant from JRE, like @EnabledOnJre(JRE.JAVA_17).

2. Step 2: Compare options

   Only @EnabledOnJre(JRE.JAVA_17) uses the correct enum constant syntax. Others use invalid or incorrect attribute names or formats.

3. Final Answer:

   @EnabledOnJre(JRE.JAVA_17) -> Option C

4. Quick Check:

   Use enum JRE.JAVA_17 inside @EnabledOnJre [OK]

Hint: Use enum JRE.JAVA_17 inside parentheses [OK]

Common Mistakes:

• Using string values instead of enum constants
• Using incorrect attribute names like version or javaVersion
• Missing the enum prefix JRE.

3. Given the test annotated with @EnabledOnJre({JRE.JAVA_11, JRE.JAVA_17}), what happens when running on Java 15?

medium

A. The test runs normally

B. The test is skipped

C. The test fails with an error

D. The test runs but logs a warning

Solution

1. Step 1: Understand the annotation behavior

   The test runs only on Java 11 or Java 17 as specified.

2. Step 2: Check Java 15 behavior

   Since Java 15 is not in the list, the test is skipped automatically.

3. Final Answer:

   The test is skipped -> Option B

4. Quick Check:

   Test runs only on specified JREs, else skipped [OK]

Hint: Test runs only on listed JREs; others skip [OK]

Common Mistakes:

• Assuming test runs on any Java version
• Expecting test to fail instead of skip
• Thinking test logs a warning when skipped

4. Identify the error in this test annotation: @EnabledOnJre(JRE.JAVA_8, JRE.JAVA_11)

medium

A. JRE.JAVA_8 is not a valid enum constant

B. The annotation cannot be used with more than one JRE

C. The annotation requires a string, not enum constants

D. Multiple JREs must be inside curly braces {}

Solution

1. Step 1: Check annotation syntax for multiple JREs

   When specifying multiple JREs, they must be enclosed in curly braces as an array.

2. Step 2: Analyze given annotation

   The annotation uses parentheses with multiple enum constants without braces, which is invalid syntax.

3. Final Answer:

   Multiple JREs must be inside curly braces {} -> Option D

4. Quick Check:

   Multiple JREs need braces: {@code @EnabledOnJre({JRE.JAVA_8, JRE.JAVA_11})} [OK]

Hint: Use curly braces for multiple JREs inside @EnabledOnJre [OK]

Common Mistakes:

• Omitting curly braces for multiple JREs
• Using strings instead of enum constants
• Thinking multiple JREs are not allowed

5. You want to write a test that runs only on Java 8, 11, and 17, but skips on all other versions. Which is the correct way to annotate the test?

hard

A. @EnabledOnJre({JRE.JAVA_8, JRE.JAVA_11, JRE.JAVA_17})

B. @EnabledOnJre(JRE.JAVA_8, JRE.JAVA_11, JRE.JAVA_17)

C. @EnabledOnJre(value = {"JAVA_8", "JAVA_11", "JAVA_17"})

D. @EnabledOnJre(versions = {JRE.JAVA_8, JRE.JAVA_11, JRE.JAVA_17})

Solution

1. Step 1: Recall correct syntax for multiple JREs

   Multiple JREs must be passed as an array inside curly braces using enum constants.

2. Step 2: Evaluate options

   @EnabledOnJre({JRE.JAVA_8, JRE.JAVA_11, JRE.JAVA_17}) correctly uses @EnabledOnJre({JRE.JAVA_8, JRE.JAVA_11, JRE.JAVA_17}). @EnabledOnJre(JRE.JAVA_8, JRE.JAVA_11, JRE.JAVA_17) misses braces, C uses strings instead of enums, D uses a wrong attribute name.

3. Final Answer:

   @EnabledOnJre({JRE.JAVA_8, JRE.JAVA_11, JRE.JAVA_17}) -> Option A

4. Quick Check:

   Use enum array with braces for multiple JREs [OK]

Hint: Use enum array with braces for multiple JREs [OK]

Common Mistakes:

• Missing curly braces for multiple JREs
• Using strings instead of enum constants
• Using incorrect attribute names like versions or value