@EnumSource for enum values in JUnit - Test Execution Trace

Test Overview

This test uses JUnit's @EnumSource to run the same test method for each value of an enum. It verifies that the enum values are correctly passed and processed in the test.

Test Code - JUnit 5

JUnit

import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.EnumSource;
import static org.junit.jupiter.api.Assertions.*;

public class TrafficLightTest {

    enum TrafficLight {
        RED, YELLOW, GREEN
    }

    @ParameterizedTest
    @EnumSource(TrafficLight.class)
    void testTrafficLightEnum(TrafficLight light) {
        assertNotNull(light);
        assertTrue(light == TrafficLight.RED || light == TrafficLight.YELLOW || light == TrafficLight.GREEN);
    }
}

Execution Trace - 5 Steps

Step	Action	System State	Assertion	Result
1	Test runner starts and identifies the parameterized test with @EnumSource for TrafficLight enum	JUnit test environment ready to run tests	—	PASS
2	Test method 'testTrafficLightEnum' runs with parameter TrafficLight.RED	Test method executing with parameter RED	assertNotNull(RED) and assertTrue(RED is one of RED, YELLOW, GREEN)	PASS
3	Test method 'testTrafficLightEnum' runs with parameter TrafficLight.YELLOW	Test method executing with parameter YELLOW	assertNotNull(YELLOW) and assertTrue(YELLOW is one of RED, YELLOW, GREEN)	PASS
4	Test method 'testTrafficLightEnum' runs with parameter TrafficLight.GREEN	Test method executing with parameter GREEN	assertNotNull(GREEN) and assertTrue(GREEN is one of RED, YELLOW, GREEN)	PASS
5	All enum values tested, test suite completes	All parameterized tests passed	—	PASS

Failure Scenario

Failing Condition: If the enum value passed to the test method is null or not one of the expected enum constants

Execution Trace Quiz - 3 Questions

What does @EnumSource(TrafficLight.class) do in this test?

A Runs the test method only once with the first enum value

B Runs the test method once for each value in the TrafficLight enum

C Skips the test method for all enum values

D Runs the test method with random enum values

Key Result

Using @EnumSource in JUnit allows easy testing of all enum values without writing separate tests, ensuring full coverage of enum-related logic.

Practice

1.

What is the main purpose of using @EnumSource in JUnit tests?

easy

A. To convert enum values to strings

B. To create a new enum type inside the test class

C. To skip tests for enum values

D. To run the test method once for each value of an enum automatically

Solution

1. Step 1: Understand the role of @EnumSource

   @EnumSource is an annotation in JUnit that provides enum values as parameters to a test method.

2. Step 2: Identify what it does in tests

   It runs the test method once for each enum constant, so all enum values are tested automatically.

3. Final Answer:

   To run the test method once for each value of an enum automatically -> Option D

4. Quick Check:

   @EnumSource runs tests per enum value = D [OK]

Hint: Remember: @EnumSource runs tests for every enum value [OK]

Common Mistakes:

• Thinking @EnumSource creates enums
• Believing it skips enum values
• Confusing it with string conversion

2.

Which of the following is the correct syntax to use @EnumSource for an enum named Status in a JUnit 5 parameterized test?

@ParameterizedTest
@EnumSource(??? )
void testStatus(Status status) { ... }

easy

A. @EnumSource(Status.class)

B. @EnumSource("Status")

C. @EnumSource(Status)

D. @EnumSource(enum = Status)

Solution

1. Step 1: Recall correct @EnumSource syntax

   The annotation requires the enum class name with .class, like Status.class.

2. Step 2: Check each option

   @EnumSource(Status.class) uses Status.class which is correct syntax. Others are invalid Java or annotation syntax.

3. Final Answer:

   @EnumSource(Status.class) -> Option A

4. Quick Check:

   Use enum class with .class in @EnumSource = A [OK]

Hint: Use EnumName.class inside @EnumSource parentheses [OK]

Common Mistakes:

• Omitting .class after enum name
• Using string instead of class reference
• Adding invalid parameters

3.

Given the enum Color { RED, GREEN, BLUE } and the test:

@ParameterizedTest
@EnumSource(Color.class)
void testColor(Color color) {
    System.out.println(color);
}

What will be the output when this test runs?

medium

A. BLUE GREEN RED

B. RED GREEN

C. RED GREEN BLUE

D. No output, test fails

Solution

1. Step 1: Understand @EnumSource behavior

   @EnumSource runs the test once for each enum constant in the order declared.

2. Step 2: Identify output from System.out.println

   Each test run prints the enum value. So output lines are RED, then GREEN, then BLUE.

3. Final Answer:

   RED GREEN BLUE -> Option C

4. Quick Check:

   Test runs once per enum value in order = C [OK]

Hint: Test runs once per enum value in declared order [OK]

Common Mistakes:

• Assuming only some enum values run
• Thinking output order is random
• Expecting test failure without reason

4.

Consider this test code snippet:

@ParameterizedTest
@EnumSource(Status.class)
void testStatus(String status) {
    assertNotNull(status);
}

What is the main problem here?

medium

A. The test method parameter type does not match the enum type

B. @EnumSource cannot be used with Status enum

C. assertNotNull is not a valid assertion

D. The test method must be static

Solution

1. Step 1: Check parameter type vs enum type

   @EnumSource(Status.class) passes enum constants of type Status, but method expects String parameter.

2. Step 2: Understand type mismatch impact

   This causes a runtime error because JUnit cannot convert Status enum to String automatically.

3. Final Answer:

   The test method parameter type does not match the enum type -> Option A

4. Quick Check:

   Parameter type must match enum type = A [OK]

Hint: Method parameter type must be the enum type used in @EnumSource [OK]

Common Mistakes:

• Using String instead of enum type as parameter
• Thinking @EnumSource only works with strings
• Assuming test method must be static

5.

You want to test only specific enum values OPEN and CLOSED from the enum TicketStatus { OPEN, IN_PROGRESS, CLOSED, REOPENED } using @EnumSource. Which is the correct way to do this?

hard

A. @EnumSource(TicketStatus.class, include = {OPEN, CLOSED})

B. @EnumSource(value = TicketStatus.class, names = {"OPEN", "CLOSED"})

C. @EnumSource(TicketStatus.class, only = {"OPEN", "CLOSED"})

D. @EnumSource(TicketStatus.class, filter = {OPEN, CLOSED})

Solution

1. Step 1: Recall how to filter enum values in @EnumSource

   @EnumSource supports a 'names' attribute to specify which enum constants to include.

2. Step 2: Check each option's syntax

   @EnumSource(value = TicketStatus.class, names = {"OPEN", "CLOSED"}) uses 'names' with string array correctly. Others use invalid or unsupported attributes.

3. Final Answer:

   @EnumSource(value = TicketStatus.class, names = {"OPEN", "CLOSED"}) -> Option B

4. Quick Check:

   Use 'names' to select enum values in @EnumSource = B [OK]

Hint: Use 'names' attribute with enum strings to filter values [OK]

Common Mistakes:

• Using unsupported attributes like include or only
• Passing enum constants instead of strings in names
• Forgetting to specify value = Enum.class