Test Coverage Improvement: internal/middleware package

Function Analyzed

• Package: internal/middleware
• Functions: applyJqSchema, savePayload, WrapToolHandler
• Previous Coverage: 75.2%
• New Coverage: 88.3%
• Complexity: High (multiple error handling branches, jq execution paths, filesystem operations)

Why These Functions?

Coverage analysis identified applyJqSchema (70%), savePayload (77.3%), and WrapToolHandler (80.5%) as the most complex under-tested functions in the middleware package. These functions handle critical error paths—jq execution failures, filesystem errors, and tool call result handling—that were completely untested.

Tests Added

TestApplyJqSchema_UncoveredPaths

• ✅ No results from jq iterator (jq empty program produces zero outputs)
• ✅ HaltError with nil value (jq halt — clean halt with no message)
• ✅ HaltError with non-nil value (jq halt_error — halt with error message)
• ✅ Generic jq type error (invalid operation on wrong type)

Tests inject custom-compiled jq programs by saving/restoring jqSchemaCode to precisely trigger each error branch.

TestSavePayload_ErrorCases

• ✅ Directory creation failure (read-only parent directory)
• ✅ File write failure (read-only target directory after MkdirAll succeeds)

TestWrapToolHandler_NilAndErrorResultCases

• ✅ Handler returns nil result (pass-through without modification)
• ✅ Handler returns IsError=true with no Go error (pass-through of MCP error result)

TestWrapToolHandler_SavePayloadFailure

• ✅ Graceful continuation when payload save fails (read-only base directory)

TestWrapToolHandler_SchemaExtractionFailure

• ✅ Falls back to original response when jq schema extraction fails (simulated compilation error)

Coverage Report

Before: 75.2% coverage
After:  88.3% coverage
Improvement: +13.1%

Function-level changes:
  applyJqSchema:   70.0% → 100.0%  (+30.0%)
  savePayload:     77.3% →  95.5%  (+18.2%)
  WrapToolHandler: 80.5% →  90.9%  (+10.4%)
```

## Test Execution

All new tests pass:

```
=== RUN   TestApplyJqSchema_UncoveredPaths
    --- PASS: TestApplyJqSchema_UncoveredPaths/no_results_from_iterator (0.00s)
    --- PASS: TestApplyJqSchema_UncoveredPaths/HaltError_with_nil_value_(clean_halt) (0.00s)
    --- PASS: TestApplyJqSchema_UncoveredPaths/HaltError_with_non-nil_value_(error_halt) (0.00s)
    --- PASS: TestApplyJqSchema_UncoveredPaths/generic_jq_error_(type_error) (0.00s)
--- PASS: TestApplyJqSchema_UncoveredPaths (0.00s)
=== RUN   TestSavePayload_ErrorCases
    --- PASS: TestSavePayload_ErrorCases/directory_creation_failure_with_read-only_parent (0.00s)
    --- PASS: TestSavePayload_ErrorCases/file_write_failure_with_read-only_directory (0.00s)
--- PASS: TestSavePayload_ErrorCases (0.00s)
=== RUN   TestWrapToolHandler_NilAndErrorResultCases
    --- PASS: TestWrapToolHandler_NilAndErrorResultCases/handler_returns_nil_result (0.00s)
    --- PASS: TestWrapToolHandler_NilAndErrorResultCases/handler_returns_IsError=true_with_no_error (0.00s)
--- PASS: TestWrapToolHandler_NilAndErrorResultCases (0.00s)
=== RUN   TestWrapToolHandler_SavePayloadFailure
--- PASS: TestWrapToolHandler_SavePayloadFailure (0.00s)
=== RUN   TestWrapToolHandler_SchemaExtractionFailure
--- PASS: TestWrapToolHandler_SchemaExtractionFailure (0.00s)

Generated by Test Coverage Improver
Next run will target the next most complex under-tested function

Generated by Test Coverage Improver