RobotnixAcademy

Unit 16 · lesson

Checkpoint 5: Tested and Refactored Program

Take a nontrivial Java program from an earlier unit and improve its structure without intentionally changing its required behavior.

Baseline

Before refactoring, submit:

  • program requirement;
  • architecture/call diagram;
  • passing behavior set;
  • at least six purposeful tests including normal, boundary, and invalid cases;
  • one preserved Version 1 defect or design problem.

The tests may run through the browser harness. Full-JDK learners should encode the appropriate set in JUnit 6 as well.

Debugging record

For the Version 1 defect, show:

reproducer
expected result
actual result
boundary trace
first divergent state
hypothesis
controlled experiment
root cause

Refactor

Choose one meaningful structural improvement, such as:

  • extract/decompose methods;
  • replace repeated variables with a collection;
  • introduce a coherent class/record;
  • move behavior to the object that owns the knowledge;
  • introduce an interface/constructor-injected collaborator;
  • replace an unjustified inheritance relationship with composition;
  • separate parsing, domain logic, and output responsibilities;
  • divide a growing program into a planned package/file structure.

Explain the design problem the refactor addresses.

Regression evidence

After refactoring:

  • rerun the original behavior set;
  • rerun the defect regression case;
  • add at least one new test made easier or more meaningful by the improved structure;
  • document any intentional behavior change separately instead of hiding it inside the refactor.

Environment evidence

State which execution lane you used.

If you used a Java 25 project environment, include project/JUnit evidence. If you used the browser core, do not claim filesystem, package, dependency, or JUnit-runner execution that did not occur.

Mastery standard

The strongest submission demonstrates three things at once:

  1. you can locate a defect from evidence rather than random edits;
  2. you can change internal design deliberately;
  3. you can use regression evidence to defend the claim that required behavior survived the change.