Fix lint errors, most_likely() tie-breaking bug, and expand test coverage to 36 tests

[Copilot]

The repo had three correctness/quality gaps: lint failures blocking CI, a behavioural mismatch between most_likely()'s documented and actual tie-breaking behaviour, and only 28 tests despite the README advertising "35+".

Fixes

quantum_simulator.py

• Removed unused imports Iterable and List from typing
• Fixed most_likely() tie-breaking — was returning the lexicographically largest bitstring on ties; now correctly returns the smallest as documented:

  # Before (returns "10" on a tie — wrong)
  return max(self.counts.items(), key=lambda item: (item[1], item[0]))[0]
  
  # After (returns "01" on a tie — matches docstring)
  best_count = max(self.counts.values())
  return min(k for k, v in self.counts.items() if v == best_count)

tests/test_quantum_simulator.py

• Renamed ambiguous variable I → identity (E741)
• Added 8 tests across 4 new classes, bringing the total to 36 and coverage to 99%:

  Class	What it covers
  TestEmptyQubits	probabilities(qubits=[]) early-return path; measure(qubits=[]) full-state collapse
  TestNonSquareUnitary	Non-square matrix guard in _apply_unitary
  TestMostLikelyTieBreaking	Two- and three-way tie resolution
  TestAdditionalCircuits	Pauli-Y, 5-qubit GHZ, Bell-state partial-measurement collapse

Original prompt

Let's ensure this repo actually does what it says it does. If not or minimal, make a plan and execute a solution please and thank you

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Project	Deployment	Actions	Updated (UTC)
blackroad-site	Ready	Preview, Comment	Mar 10, 2026 9:00am

[Copilot]

Pull request overview

This PR addresses CI quality/correctness gaps in the quantum circuit simulator by aligning MeasurementResult.most_likely() behavior with its documented tie-breaking rule, cleaning up lint issues, and expanding test coverage.

Changes:

• Fix MeasurementResult.most_likely() to break ties by choosing the lexicographically smallest bitstring.
• Resolve a Ruff E741 lint issue by renaming an ambiguous variable in tests and add new tests for edge cases and additional circuits.
• (Unintended) adds a .coverage artifact file to the repository.

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 1 comment.

File	Description
quantum_simulator.py	Removes unused typing imports and corrects most_likely() tie-breaking logic to match the docstring.
tests/test_quantum_simulator.py	Fixes an ambiguous variable name and adds additional tests to improve coverage across edge cases and circuits.
.coverage	Adds a local coverage data artifact (should not be committed).

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[Copilot]

Test name and docstring disagree: the function name says qubit1 collapses qubit0, but the test measures qubit 0 and asserts the full state collapses accordingly. Rename the test to match the behavior being validated to avoid confusion when reading failures.

[Copilot]

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