[test-improver] Improve tests for server circuit breaker

[github-actions]

File Analyzed

• Test File: internal/server/circuit_breaker_test.go
• Package: internal/server
• Lines Added: +75

Improvements Made

1. Increased Coverage

Five previously uncovered branches in circuit_breaker.go are now exercised:

• ✅ RecordSuccess from OPEN state — covers the else if prev != circuitClosed branch, which fires when an in-flight request completes successfully after the circuit was already opened by a concurrent request
• ✅ Allow in HALF-OPEN with probeInFlight=false — covers the defensive fallback that permits a request through when the probe flag was reset without a state transition (the comment in code says "This shouldn't normally happen")
• ✅ extractRateLimitErrorText with non-map content items — covers the continue branch when a content array element is not a map[string]interface{} (e.g. a raw string)
• ✅ isRateLimitToolResult with non-map content items — same branch, parallel function
• ✅ parseRateLimitResetFromText without a terminator — covers the end < 0 branch when the seconds value has no trailing s, ], or ) delimiter (e.g. "rate reset in 42")

2. Coverage Improvements (circuit_breaker.go)

Function	Before	After
Allow	90.0%	95.0%
RecordSuccess	91.7%	100.0%
extractRateLimitErrorText	90.9%	100.0%
isRateLimitToolResult	93.8%	100.0%
parseRateLimitResetFromText	91.7%	100.0%

Overall internal/server package: 88.8% → 89.2%

3. Cleaner & More Stable Tests

• ✅ All new tests use t.Parallel() consistent with the existing style
• ✅ New tests follow the same table-driven and subtest patterns already established in the file
• ✅ TestCircuitBreaker_HalfOpenAllowsWhenNoProbeInFlight directly manipulates internal state via the exported mutex to set up the edge-case scenario without timing dependencies

Test Execution

All tests pass:

ok  github.com/github/gh-aw-mcpg/internal/server  4.460s

Note: TestFetchAndFixSchema_NetworkError in internal/config is a pre-existing failure (confirmed by checking main before this change) and is unrelated to these modifications.

Why These Changes?

The circuit_breaker.go functions RecordSuccess, extractRateLimitErrorText, isRateLimitToolResult, and parseRateLimitResetFromText each had minor coverage gaps caused by defensive/error branches that are difficult to trigger through normal code flow. These branches protect against edge cases (in-flight requests completing after circuit open, malformed content arrays, truncated error strings) and are important to verify correct behavior. The new tests exercise each gap directly and confirm the expected fallback behavior.

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[Copilot]

Pull request overview

This PR improves branch coverage for the server rate-limit circuit breaker by adding targeted tests for defensive/edge-case paths in the circuit breaker and rate-limit parsing helpers.

Changes:

• Add test coverage for skipping non-map content entries in rate-limit tool result parsing/extraction.
• Add test coverage for rate-limit reset parsing when the pattern has no terminator.
• Add tests for circuit breaker edge states: RecordSuccess() when OPEN and Allow() when HALF-OPEN with probeInFlight=false.

Show a summary per file

File	Description
internal/server/circuit_breaker_test.go	Adds new table/subtests to exercise previously uncovered defensive branches in circuit breaker logic and rate-limit text parsing.

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• Files reviewed: 1/1 changed files
• Comments generated: 1