Testing multiple exceptions in JUnit - Framework Patterns

Framework Mode - Testing multiple exceptions

Folder Structure

src/
└── test/
    └── java/
        └── com/
            └── example/
                ├── exceptions/
                │   └── CustomException.java
                ├── utils/
                │   └── ExceptionUtils.java
                ├── pages/
                │   └── SamplePage.java
                └── tests/
                    └── ExceptionTests.java

Test Framework Layers

• Test Classes: Located in tests/, contain JUnit test methods that verify multiple exceptions using assertThrows or assertAll.
• Page Objects / Business Logic: In pages/ or utils/, contain methods that may throw different exceptions.
• Custom Exceptions: Defined in exceptions/ folder for specific error cases.
• Utilities: Helper methods for exception handling or test data setup.
• Configuration: Externalized configs for environment or test parameters (not shown here).

Configuration Patterns

• Use src/test/resources for environment-specific properties (e.g., test data, exception messages).
• Use Maven or Gradle profiles to switch environments if needed.
• Keep exception messages or codes configurable to verify in tests.
• JUnit 5 annotations and extensions configured in pom.xml or build.gradle.

Test Reporting and CI/CD Integration

• JUnit 5 generates XML reports consumable by CI tools like Jenkins or GitHub Actions.
• Use Surefire or Gradle test task to run tests and produce reports.
• Reports show which exception tests passed or failed with stack traces.
• Integrate with code coverage tools (e.g., JaCoCo) to ensure exception paths are tested.
• Fail build on test failures to maintain quality.

Best Practices for Testing Multiple Exceptions

• Use assertThrows for each expected exception separately to keep tests clear.
• Use assertAll to group multiple exception assertions in one test method.
• Define custom exceptions to make error cases explicit and testable.
• Keep exception messages consistent and verify them in assertions for clarity.
• Write small focused tests for each exception scenario to simplify debugging.

Self Check

Where would you add a new test method that verifies a third custom exception in this framework structure?

Key Result

Organize tests to verify multiple exceptions clearly using JUnit's assertThrows and assertAll within a structured src/test/java folder.

Practice

1.

Which JUnit method is best to test that a specific exception is thrown by a method?

easy

A. assertThrows()

B. assertEquals()

C. assertTrue()

D. assertNull()

Solution

1. Step 1: Understand the purpose of assertThrows()

   This method checks if a specific exception is thrown when running a code block.

2. Step 2: Compare with other assertion methods

   assertEquals() checks values, assertTrue() checks boolean conditions, and assertNull() checks for null values, none test exceptions.

3. Final Answer:

   assertThrows() -> Option A

4. Quick Check:

   Test exceptions with assertThrows() [OK]

Hint: Use assertThrows() to check exceptions directly [OK]

Common Mistakes:

• Using assertEquals() to test exceptions
• Trying to catch exceptions manually in tests
• Confusing assertTrue() with exception testing

2.

Which of the following is the correct syntax to test that IllegalArgumentException is thrown by myMethod() in JUnit 5?

?

easy

A. assertThrows(myMethod(), IllegalArgumentException.class);

B. assertThrows(() -> myMethod(), IllegalArgumentException.class);

C. assertThrows(IllegalArgumentException.class, () -> myMethod());

D. assertThrows(IllegalArgumentException, myMethod());

Solution

1. Step 1: Recall assertThrows() method signature

   The correct order is the exception class first, then a lambda with the code to test.

2. Step 2: Check each option's syntax

   assertThrows(IllegalArgumentException.class, () -> myMethod()); matches the correct syntax: assertThrows(Exception.class, () -> method());. Others have wrong order or missing lambda.

3. Final Answer:

   assertThrows(IllegalArgumentException.class, () -> myMethod()); -> Option C

4. Quick Check:

   Exception class first, then lambda [OK]

Hint: Exception class first, then lambda expression [OK]

Common Mistakes:

• Swapping parameters order in assertThrows
• Not using a lambda expression
• Passing method call instead of lambda

3.

Given the following JUnit 5 test code, what will be the test result?

void testMultipleExceptions() {
  assertThrows(NullPointerException.class, () -> { throw new NullPointerException(); });
  assertThrows(IllegalStateException.class, () -> { throw new IllegalArgumentException(); });
}

medium

A. Test fails because second assertThrows expects IllegalStateException but gets IllegalArgumentException

B. Test passes because both exceptions are thrown

C. Test fails because NullPointerException is not thrown

D. Test passes because assertThrows ignores exception type

Solution

1. Step 1: Analyze first assertThrows

   It expects NullPointerException and throws NullPointerException, so it passes.

2. Step 2: Analyze second assertThrows

   It expects IllegalStateException but throws IllegalArgumentException, so it fails.

3. Final Answer:

   Test fails because second assertThrows expects IllegalStateException but gets IllegalArgumentException -> Option A

4. Quick Check:

   Expected exception must match thrown exception [OK]

Hint: Exception types must match exactly in assertThrows [OK]

Common Mistakes:

• Assuming any exception passes assertThrows
• Ignoring mismatch in exception types
• Thinking assertThrows catches all exceptions

4.

Identify the error in the following JUnit 5 test code that tries to test two exceptions:

@Test
void testExceptions() {
  assertThrows(NullPointerException.class, () -> method1());
  assertThrows(IllegalArgumentException.class, () -> method2());
  assertThrows(IllegalStateException.class, () -> method3());
}

Assuming method2() throws IllegalStateException instead of IllegalArgumentException.

medium

A. The test will pass because all exceptions are thrown

B. The second assertThrows will fail because expected and actual exceptions differ

C. The test will fail because assertThrows cannot be called multiple times

D. The test will fail because method3() is not called

Solution

1. Step 1: Check expected vs actual exceptions for method2()

   Expected is IllegalArgumentException but actual thrown is IllegalStateException, so assertThrows fails.

2. Step 2: Confirm other assertThrows calls

   Calls for method1() and method3() are correct or irrelevant to this error.

3. Final Answer:

   The second assertThrows will fail because expected and actual exceptions differ -> Option B

4. Quick Check:

   Expected exception must match thrown exception [OK]

Hint: Check expected vs actual exception types carefully [OK]

Common Mistakes:

• Assuming multiple assertThrows calls cause failure
• Ignoring mismatch in exception types
• Thinking assertThrows tests method calls, not exceptions

5.

You want to test that a method process() throws either IOException or TimeoutException depending on conditions. Which is the best way to write JUnit 5 tests for both exceptions?

hard

A. Use one assertThrows with both exceptions listed together

B. Use assertThrows only for the first exception and ignore the second

C. Catch exceptions manually inside one test and assert their types

D. Write two separate tests each using assertThrows for one exception

Solution

1. Step 1: Understand assertThrows usage

   assertThrows tests one exception type per call; it cannot test multiple exceptions at once.

2. Step 2: Best practice for multiple exceptions

   Write separate tests for each expected exception to keep tests clear and focused.

3. Final Answer:

   Write two separate tests each using assertThrows for one exception -> Option D

4. Quick Check:

   One assertThrows per exception per test [OK]

Hint: Test each exception in its own assertThrows call [OK]

Common Mistakes:

• Trying to test multiple exceptions in one assertThrows
• Catching exceptions manually instead of using assertThrows
• Ignoring one exception in tests