new-challenge

name	new-challenge
description	Generate a fresh Java coding exercise (stub + failing JUnit tests) on a given topic for the user to solve on their own, TDD-style. Use when the user asks for a new challenge, exercise, or technical test on any Java/Spring/DSA/design topic.

Skill: new-challenge

Create a new self-contained exercise in the java-mastery repo, following the repo's TDD learning loop. The user solves it alone — never provide the solution up front.

Input

$ARGUMENTS = a topic and optional difficulty, e.g. "streams grouping", "binary tree traversal medium", "builder pattern". If empty, pick the next logical topic from the tracker in the root README.md.

Steps

1. Determine the target module (e.g. m05_streams_functional). Create the package folders under src/main/java/com/mastery/<module>/exercises/ and the test folder under src/test/java/com/mastery/<module>/ if they don't exist.
2. Write an exercise class:
   • Rich Javadoc describing the task, rules, edge cases, and hints (concepts, not answers).
   • Public method signatures with // TODO and throw new UnsupportedOperationException(...).
3. Write a JUnit 5 test class (the technical test):
   • Use AssertJ (assertThat) and @DisplayName.
   • Cover happy paths, edge cases (empty, null, negatives, boundaries), and at least one tricky case. Prefer @ParameterizedTest where it fits.
   • Tests must currently FAIL (red) because of the stub.
4. Run mvn -Dtest=<TestClass> test to confirm it compiles and fails for the right reason (assertion / UnsupportedOperationException), not a compile error.
5. Report the file paths, the concepts covered, and the command to run. Do NOT reveal the implementation.

Difficulty guidance

• easy: 1 method, single concept.
• medium: 2–3 methods, an edge case that bites, or a small algorithm.
• hard: interview-grade — non-trivial algorithm, performance constraint, or multi-class design.