@EnumSource for enum values in JUnit

Introduction

@EnumSource helps run the same test with all values of an enum. This saves time and avoids writing many similar tests.

You want to check that a method works correctly for every value in an enum.

You have a list of fixed options and want to test each one automatically.

You want to avoid repeating similar test code for each enum value.

Syntax

JUnit

@ParameterizedTest
@EnumSource(EnumClassName.class)
void testMethod(EnumClassName value) {
    // test code using value
}

The test method receives each enum value one by one.

Use @EnumSource with the enum class name to specify which enum to use.

Examples

This test runs once for each Color enum value, checking it is not null.

JUnit

@ParameterizedTest
@EnumSource(Color.class)
void testColor(Color color) {
    assertNotNull(color);
}

This test runs only for SMALL and MEDIUM enum values of Size.

JUnit

@ParameterizedTest
@EnumSource(value = Size.class, names = {"SMALL", "MEDIUM"})
void testSize(Size size) {
    assertTrue(size == Size.SMALL || size == Size.MEDIUM);
}

Sample Program

This test runs three times, once for each day in the Day enum. It checks that the day value is not null.

JUnit

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

enum Day {
    MONDAY, TUESDAY, WEDNESDAY
}

public class EnumSourceTest {

    @ParameterizedTest
    @EnumSource(Day.class)
    void testDayIsNotNull(Day day) {
        assertNotNull(day);
    }
}

Important Notes

You can filter enum values using the 'names' attribute in @EnumSource.

Use @EnumSource when you want to test all or some enum values without writing loops.

Summary

@EnumSource runs tests for each enum value automatically.

It helps test all fixed options easily and clearly.

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