[test-improver] Improve tests for config tracing package

[github-actions]

Test Improvements: config_tracing_test.go

File Analyzed

• Test File: internal/config/config_tracing_test.go
• Package: internal/config
• Lines Added: +123 lines (11 new test functions)

Improvements Made

1. Increased Coverage

• ✅ GetSampleRate on nil receiver — prevented panic, returns default (was untested)
• ✅ GetSampleRate with nil SampleRate field — returns default (was untested)
• ✅ GetSampleRate with explicit 0.0 — distinct from unset, returns 0.0 (was untested)
• ✅ applyDefaults when cfg.Gateway is nil — no panic (was untested)
• ✅ applyDefaults when cfg.Gateway.Tracing is nil — no panic (was untested)
• ✅ applyDefaults when ServiceName is already set — preserves custom value (was untested)
• ✅ StdinConverter full field mapping from StdinOpenTelemetryConfig → TracingConfig
• ✅ StdinConverter default ServiceName applied when stdin value is empty
• ✅ StdinConverter early-return when stdinCfg.Gateway is nil
• ✅ StdinConverter early-return when stdinCfg.Gateway.OpenTelemetry is nil

Previous Coverage (config_tracing.go functions):

• GetSampleRate: 66.7%
• init: 53.8%

New Coverage:

• GetSampleRate: 100.0%
• init: 92.3%

2. Better Testing Patterns

• ✅ Each new test targets exactly one behavior with a descriptive name
• ✅ require.NotPanics used for nil-safety assertions
• ✅ require.NotNil guards before accessing pointer fields in stdin converter tests
• ✅ Test names follow TestType_Scenario convention

Test Execution

All new and existing tests pass (pre-existing TestFetchAndFixSchema_NetworkError failure is unrelated — network-dependent test that fails in CI sandbox):

=== RUN   TestGetSampleRate_NilReceiver
--- PASS: TestGetSampleRate_NilReceiver (0.00s)
=== RUN   TestGetSampleRate_NilSampleRate
--- PASS: TestGetSampleRate_NilSampleRate (0.00s)
=== RUN   TestGetSampleRate_ZeroExplicitRate
--- PASS: TestGetSampleRate_ZeroExplicitRate (0.00s)
=== RUN   TestTracingDefaults_ServiceNameAlreadySet
--- PASS: TestTracingDefaults_ServiceNameAlreadySet (0.00s)
=== RUN   TestTracingDefaults_NilGateway
--- PASS: TestTracingDefaults_NilGateway (0.00s)
=== RUN   TestTracingDefaults_NilTracing
--- PASS: TestTracingDefaults_NilTracing (0.00s)
=== RUN   TestStdinConverter_OTelConfig
--- PASS: TestStdinConverter_OTelConfig (0.00s)
=== RUN   TestStdinConverter_OTelConfig_DefaultsServiceName
--- PASS: TestStdinConverter_OTelConfig_DefaultsServiceName (0.00s)
=== RUN   TestStdinConverter_OTelConfig_NilGateway
--- PASS: TestStdinConverter_OTelConfig_NilGateway (0.00s)
=== RUN   TestStdinConverter_OTelConfig_NilOpenTelemetry
--- PASS: TestStdinConverter_OTelConfig_NilOpenTelemetry (0.00s)

Why These Changes?

config_tracing_test.go had clear coverage gaps: GetSampleRate was only tested with a non-nil pointer (missing nil receiver and nil-field cases), and the init-registered callbacks for DefaultsSetter and StdinConverter had uncovered early-return paths and the full converter mapping path was untested. These are important paths — nil-safety on a value receiver method and correct behavior of the stdin JSON config pipeline — that could regress silently without tests.

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[Copilot]

Pull request overview

This PR expands unit test coverage for the internal/config tracing configuration feature, focusing on nil-safety and stdin (JSON) conversion behavior around OpenTelemetry tracing settings.

Changes:

• Adds GetSampleRate coverage for nil receiver / nil SampleRate / explicit 0.0 cases.
• Adds coverage for tracing defaults behavior, including preserving an explicitly-set ServiceName.
• Adds coverage for the init-registered stdin converter mapping and its early-return paths.

Show a summary per file

File	Description
internal/config/config_tracing_test.go	Adds targeted tests for tracing sample-rate behavior, default application, and stdin converter field mapping / nil-safety.

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• Files reviewed: 1/1 changed files
• Comments generated: 2

[lpcox]

@copilot address the review feedback and fix the ci failures

[Copilot]

@copilot address the review feedback and fix the ci failures

Done in c4e578a:

• CI lint failure: Fixed formatting in internal/server/circuit_breaker.go, circuit_breaker_test.go, and internal/strutil/format_duration_test.go (pre-existing gofmt issues in those files).
• Review feedback on TestTracingDefaults_NilGateway: Updated to call cfg.EnsureGatewayDefaults() instead of applyDefaults directly — this reflects the real call pattern used by production loaders and also verifies that EnsureGatewayDefaults initialises the Gateway field when nil.