Yuvraj Singh — R45-T034: Test an invariant of Combination (Combination.java) [src/main/java/com/thealgorithms/backtracking/Combination.java] #34

Student: Yuvraj Singh

Task: R45-T034 · 4 of 10
Repository: https://github.com/S-AI-Projects/TheAlgorithms-Java
Assigned working branch: student/e26b07f0666

Goal

Work on src/main/java/com/thealgorithms/backtracking/Combination.java. Add a property test around Combination: Preserve the documented output type, shape, ordering and input-mutation behavior; compare fresh equivalent inputs under controlled external state. Fixture: Use the smallest valid input and one ordinary input for Combination from src/main/java/com/thealgorithms/backtracking/Combination.java. Write the literal inputs and independently calculated expected outputs in the tests before editing the implementation. The check must name the source line establishing each precondition.

Steps

1. Read src/main/java/com/thealgorithms/backtracking/Combination.java, especially Combination near line 13. Record its public inputs, result, mutation behavior and any external dependencies before changing it.
2. Use the fixture to establish the invariant on understandable examples. Use the smallest valid input and one ordinary input for Combination from src/main/java/com/thealgorithms/backtracking/Combination.java. Write the literal inputs and independently calculated expected outputs in the tests before editing the implementation. The check must name the source line establishing each precondition.
3. Generate at least 100 bounded valid cases with a fixed seed; restrict the generator to the actual input domain and retain a readable small case.
4. Implement work/R45-T034/check.py as a focused runner that executes the new checks and propagates failures. Native check to incorporate: mvn test (JDK 21 as specified in pom.xml); use JUnit in the corresponding src/test/java package. Record the actual command and nonzero test count.
5. Create the checks specified below and run python3 work/R45-T034/check.py. Save inputs, expected versus actual results and tool versions in work/R45-T034/; a check must exit non-zero when an assertion fails.
6. Commit the repository change on branch R45-T034; prepare a PR to the organisation fork explaining the result and linking the checks. Keep each task independently reviewable. Remove work/R45-T034/ from a later upstream branch.

Done when

☐ The checked behavior is tied to Combination in src/main/java/com/thealgorithms/backtracking/Combination.java; every assertion has an explicit expected value.
☐ Use the smallest valid input and one ordinary input for Combination from src/main/java/com/thealgorithms/backtracking/Combination.java. Write the literal inputs and independently calculated expected outputs in the tests before editing the implementation. The check must name the source line establishing each precondition.
☐ Existing supported behavior and the public interface are preserved unless a failing regression demonstrates and documents a defect.
☐ The generator never relies on undefined input behavior; the invariant is justified in the PR.
☐ The checks fail when the relevant invariant is deliberately broken in a temporary copy.

Submission checklist

• Complete this task and its checks.
• Add the required evidence and link your pull request here.
• Select this S-AI-Projects fork as the PR base repository.
• Request instructor review.

Keep this PR focused on this task. Do not submit assignment PRs to the upstream repository.