@EnumSource for enum values in JUnit - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the @EnumSource annotation in JUnit?

@EnumSource is used to run a parameterized test with all or some values of an enum. It helps test methods with enum inputs easily.

beginner

How do you specify which enum to use with @EnumSource?

<p>You provide the enum class as a parameter, like <code>@EnumSource(MyEnum.class)</code>. This tells JUnit to use all values of <code>MyEnum</code> for the test.</p>

intermediate

How can you run a test with only specific enum values using @EnumSource?

Use the names attribute to list enum constants you want, e.g., @EnumSource(value = MyEnum.class, names = {"VALUE1", "VALUE2"}).

intermediate

What happens if you use @EnumSource without specifying an enum class?

<p>JUnit expects the parameter type of the test method to be an enum. It uses that enum class automatically.</p>

beginner

Write a simple example of a JUnit test method using @EnumSource to test all values of an enum Day.

enum Day { MONDAY, TUESDAY, WEDNESDAY }

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

What does @EnumSource(MyEnum.class) do in a JUnit test?

A Runs the test with all enum values except the first

B Runs the test once for each value in MyEnum

C Runs the test only once with the first enum value

D Runs the test with no enum values

@EnumSource(MyEnum.class) runs the test once for each enum constant in MyEnum.

How do you run a test with only specific enum values using @EnumSource?

A Use the <code>names</code> attribute with the enum constants you want

B Use <code>excludeNames</code> attribute

C Use <code>value</code> attribute with a list of values

D You cannot filter enum values with <code>@EnumSource</code>

The names attribute lets you specify which enum constants to include.

If the test method parameter type is an enum, can you omit the enum class in @EnumSource?

A Only if the enum is public

B No, you must always specify the enum class

C Yes, JUnit infers the enum class from the parameter type

D Only if the enum has less than 5 values

JUnit can infer the enum class from the test method parameter type if you omit it.

What type of test is @EnumSource mainly used with?

A Unit tests without parameters

B Performance tests

C Integration tests

D Parameterized tests

@EnumSource is designed for parameterized tests to supply enum values.

Which of these is a valid way to use @EnumSource?

A @EnumSource(value = Status.class, names = {"ACTIVE", "INACTIVE"})

B @EnumSource(Status.ACTIVE, Status.INACTIVE)

C @EnumSource(Status)

D @EnumSource(names = Status.class)

Option A correctly uses value and names attributes.

Explain how @EnumSource works in JUnit parameterized tests and how you can select specific enum values.

Think about how JUnit uses enum values to run tests multiple times.

Describe a simple example of a JUnit test method using @EnumSource with an enum parameter.

Imagine testing all days of the week using an enum.

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