Test Coverage Improvement: parseToolArguments and related methods

Functions Analyzed

• Package: internal/server
• Primary Target: parseToolArguments — 0% previous coverage
• Additional Coverage: GetPayloadSizeThreshold, GetServerStatus, IsDIFCEnabled, SetHTTPShutdown, GetHTTPShutdown
• Complexity: Medium–High (multiple branches, JSON parsing, config fallback logic)

Why These Functions?

parseToolArguments in unified.go had zero test coverage despite being a critical function that parses MCP tool arguments for registered handlers (including sys___init). It has three distinct code paths:

1. nil arguments → returns empty map (no-arg tool calls)
2. Valid JSON object → unmarshals to map[string]interface{}
3. Invalid JSON → wraps and returns an error

The additional functions (GetPayloadSizeThreshold, GetServerStatus, IsDIFCEnabled, SetHTTPShutdown/GetHTTPShutdown) are direct getters/setters on UnifiedServer that were reachable in production but had no unit tests exercising them directly.

Tests Added

TestParseToolArguments (16 table-driven cases):

• ✅ Nil arguments → empty map
• ✅ Empty JSON object {}
• ✅ Simple string, multiple strings, numeric, boolean arguments
• ✅ Nested object and array arguments
• ✅ JSON null value for a key
• ✅ Mixed argument types (string + int + bool + array)
• ✅ Invalid JSON → error with expected message prefix
• ✅ JSON array / string / number at top level → error
• ✅ Empty string value, Unicode content

TestParseToolArguments_NilArgumentsAlwaysReturnsNewMap:

• ✅ Verifies two calls with nil args produce independent maps (mutation isolation)

TestParseToolArguments_ErrorWrapping:

• ✅ Verifies error is wrapped with "failed to parse arguments:"

TestGetPayloadSizeThreshold (4 sub-tests):

• ✅ Custom positive threshold used directly
• ✅ Zero threshold falls back to DefaultPayloadSizeThreshold
• ✅ Nil gateway config falls back to default
• ✅ Large custom threshold (10 MB)

TestGetServerStatus (3 table-driven + 1 mutation isolation):

• ✅ Zero, one, and multiple configured servers
• ✅ All entries report "running" status
• ✅ Returned map is independent (mutations don't affect future calls)

TestIsDIFCEnabled:

• ✅ DIFC disabled (default) and enabled via config

TestSetAndGetHTTPShutdown (5 sub-tests):

• ✅ Nil by default, set/get roundtrip, override, reset to nil, error propagation

Coverage Report

Before:
  parseToolArguments              0%
  GetPayloadSizeThreshold         0%
  GetServerStatus                 0%
  IsDIFCEnabled                   0%
  SetHTTPShutdown / GetHTTPShutdown  0%

After:
  parseToolArguments              100%  (all 3 branches)
  GetPayloadSizeThreshold         100%  (all 3 config paths)
  GetServerStatus                 100%
  IsDIFCEnabled                   100%
  SetHTTPShutdown / GetHTTPShutdown  100%

Test File

• File: internal/server/parse_tool_arguments_test.go
• Package: package server (same package, tests internal functions)
• Pattern: table-driven tests with t.Run() sub-tests, testify assert/require

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