[test-improver] Improve tests for tracing package (#7740)

# Test Improvements: `provider_internal_test.go`

## File Analyzed

- **Test File**: `internal/tracing/provider_internal_test.go`
- **Package**: `internal/tracing`
- **Lines of Code**: 52 → 117 (+65 lines)

## Improvements Made

### 1. Increased Coverage

- ✅ Added `TestGenerateRandomSpanID`: verifies the happy path — produces
a valid non-zero 8-byte span ID and that successive calls yield distinct
values
- ✅ Added `TestGenerateRandomSpanID_Error`: injects a failing
`crypto/rand.Reader` to cover the previously dead error-return path in
`generateRandomSpanID`
- ✅ Added `TestParentContext_RandomSpanIDFailure`: triggers the `genErr
!= nil` branch in `ParentContext` (lines 322–325 of `provider.go`) by
breaking the random source, verifying the original context is returned
unchanged

| Function | Before | After |
|---|---|---|
| `generateRandomSpanID` | 83.3% | 100% |
| `ParentContext` | 92.6% | 100% |
| **Package total** | **95.2%** | **96.2%** |

### 2. Better Testing Patterns

- ✅ Error-path injection via `errorReader` struct (same pattern as
`auth/header_test.go`) to test unreachable crypto-failure branches
- ✅ Tests that must not run in parallel (global `rand.Reader` mutation)
are explicitly left non-parallel with a comment explaining why
- ✅ `require.NoError` / `require.Error` for blocking assertions,
`assert.*` for non-blocking checks — consistent with project conventions
- ✅ `t.Parallel()` on the pure happy-path test that has no global side
effects

## Test Execution

All tests pass:
```
ok  	github.com/github/gh-aw-mcpg/internal/tracing	0.023s	coverage: 96.2% of statements
```

## Why These Changes?

`provider_internal_test.go` was a thin 52-line file that only tested
`mergeOTLPHeaders`. The two functions with coverage gaps —
`generateRandomSpanID` (83.3%) and `ParentContext` (92.6%) — had
unreachable error paths that require `crypto/rand` failure injection.
Since the test file is in package `tracing` (not `tracing_test`), it has
direct access to the unexported `generateRandomSpanID` and can inject
the `rand.Reader` failure needed to exercise both error branches. The
improvements follow the exact same `errorReader` / `rand.Reader` swap
pattern already established in `internal/auth/header_test.go`.

---
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Author: lpcox

internal/tracing/provider_internal_test.go

@@ -1,9 +1,16 @@
 package tracing
 
 import (
+	"context"
+	"crypto/rand"
+	"errors"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"go.opentelemetry.io/otel/trace"
+
+	"github.com/github/gh-aw-mcpg/internal/config"
 )
 
 func TestMergeOTLPHeaders(t *testing.T) {
@@ -50,3 +57,61 @@ func TestMergeOTLPHeaders(t *testing.T) {
 		})
 	}
 }
+
+// TestGenerateRandomSpanID verifies that generateRandomSpanID produces a valid,
+// non-zero 8-byte span ID and that successive calls produce distinct values.
+func TestGenerateRandomSpanID(t *testing.T) {
+	t.Parallel()
+
+	id, err := generateRandomSpanID()
+	require.NoError(t, err, "generateRandomSpanID should not fail with a healthy rand.Reader")
+	assert.NotEqual(t, trace.SpanID{}, id, "generated span ID should be non-zero")
+
+	id2, err := generateRandomSpanID()
+	require.NoError(t, err)
+	assert.NotEqual(t, id, id2, "successive calls should produce distinct span IDs")
+}
+
+// errorReader is an io.Reader that always returns the configured error.
+type errorReader struct{ err error }
+
+func (r *errorReader) Read(_ []byte) (int, error) { return 0, r.err }
+
+// TestGenerateRandomSpanID_Error verifies that generateRandomSpanID propagates
+// errors from the underlying random source and returns a zero span ID.
+// Must NOT run in parallel: temporarily replaces the global crypto/rand.Reader.
+func TestGenerateRandomSpanID_Error(t *testing.T) {
+	syntheticErr := errors.New("synthetic entropy failure")
+
+	origReader := rand.Reader
+	rand.Reader = &errorReader{err: syntheticErr}
+	defer func() { rand.Reader = origReader }()
+
+	id, err := generateRandomSpanID()
+
+	assert.Equal(t, trace.SpanID{}, id, "span ID should be zero on error")
+	require.Error(t, err, "should return an error when the random source fails")
+	assert.ErrorIs(t, err, syntheticErr, "error should wrap the underlying source error")
+	assert.Contains(t, err.Error(), "failed to generate random span ID")
+}
+
+// TestParentContext_RandomSpanIDFailure verifies that ParentContext returns the
+// original context unchanged when generateRandomSpanID fails due to a broken
+// random source. This covers the genErr != nil branch (lines 322–325 of provider.go).
+// Must NOT run in parallel: temporarily replaces the global crypto/rand.Reader.
+func TestParentContext_RandomSpanIDFailure(t *testing.T) {
+	ctx := context.Background()
+	cfg := &config.TracingConfig{
+		TraceID: "4bf92f3577b34da6a3ce929d0e0e4736", // valid 32-char hex (non-zero)
+		// SpanID intentionally absent so ParentContext must generate one
+	}
+
+	origReader := rand.Reader
+	rand.Reader = &errorReader{err: errors.New("entropy unavailable")}
+	defer func() { rand.Reader = origReader }()
+
+	parentCtx := ParentContext(ctx, cfg)
+
+	assert.True(t, ctx == parentCtx,
+		"ParentContext must return the original context when random span ID generation fails")
+}