[test-improver] Improve tests for sys package (#7848)

# Test Improvements: `internal/sys/container_test.go` +
`container_detect_test.go`

## File Analyzed

- **Test Files**: `internal/sys/container_test.go`,
`internal/sys/container_detect_test.go`
- **Package**: `internal/sys`

## Improvements Made

### 1. Scanner-overflow coverage (new test case)

Added a test case `"single line exceeding scanner buffer limit returns
empty string"` to `TestExtractContainerIDFromContent`. This covers the
previously-untested `scanner.Err() != nil` branch in
`extractContainerIDFromContent` (triggered when a single line exceeds
`bufio.MaxScanTokenSize` = 65,536 bytes):

```go
{
    name:  "single line exceeding scanner buffer limit returns empty string",
    input: strings.Repeat("x", bufio.MaxScanTokenSize+1),
    want:  "",
},
```

### 2. Parallel test execution

Added `t.Parallel()` to all pure-function tests (safe to run
concurrently — no environment mutation, no shared state):

- `TestExtractContainerIDFromContent` + all 16 subtests
- `TestContainsAny_Helper` + all subtests  
- 6 × `TestExtractContainerIDFromCgroupFiles_*` tests in
`container_detect_test.go` (temp-file only, no `t.Setenv`)

### 3. Increased Coverage

- **Previous coverage**: `extractContainerIDFromContent` → 92.3%,
package total → 98.9%
- **New coverage**: `extractContainerIDFromContent` → **100.0%**,
package total → **100.0%**
- **Improvement**: +1.1% package, +7.7% on the targeted function

## Test Execution

```
ok  github.com/github/gh-aw-mcpg/internal/sys  coverage: 100.0% of statements
```

All tests pass with `-race` flag enabled. Tests run multiple times with
consistent results.

## Why These Changes?

`extractContainerIDFromContent` used `bufio.Scanner` to parse cgroup
content but the error path (`scanner.Err() != nil`) was never exercised
— it requires a line longer than 64 KiB, an unusual but valid edge case.
Adding the overflow test ensures the error path is verified. The
parallelism additions are low-risk improvements to pure-function tests,
reducing wall-clock test time with no behavior changes.

---
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*Focuses on better patterns, increased coverage, and more stable tests*




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Author: lpcox

internal/sys/container_detect_test.go

@@ -217,6 +217,8 @@ func TestDetectContainerIDWithPaths_MultipleIndicatorLines(t *testing.T) {
 // TestExtractContainerIDFromCgroupFiles_ReturnsFirstFound tests that
 // extractContainerIDFromCgroupFiles returns the ID from the first file that yields one.
 func TestExtractContainerIDFromCgroupFiles_ReturnsFirstFound(t *testing.T) {
+	t.Parallel()
+
 	dir := t.TempDir()
 
 	first := writeTempFile(t, dir, "cgroup1", "0::/docker/aabbccdd1234\n")
@@ -229,6 +231,8 @@ func TestExtractContainerIDFromCgroupFiles_ReturnsFirstFound(t *testing.T) {
 // TestExtractContainerIDFromCgroupFiles_SkipsEmptyFile tests that a file with
 // no container ID is skipped and the next file is tried.
 func TestExtractContainerIDFromCgroupFiles_SkipsEmptyFile(t *testing.T) {
+	t.Parallel()
+
 	dir := t.TempDir()
 
 	noMatch := writeTempFile(t, dir, "cgroup1", "0::/user.slice\n")
@@ -241,6 +245,8 @@ func TestExtractContainerIDFromCgroupFiles_SkipsEmptyFile(t *testing.T) {
 // TestExtractContainerIDFromCgroupFiles_AllEmpty tests that "" is returned when
 // no files yield a container ID.
 func TestExtractContainerIDFromCgroupFiles_AllEmpty(t *testing.T) {
+	t.Parallel()
+
 	dir := t.TempDir()
 
 	f1 := writeTempFile(t, dir, "cgroup1", "0::/\n")
@@ -252,19 +258,22 @@ func TestExtractContainerIDFromCgroupFiles_AllEmpty(t *testing.T) {
 
 // TestExtractContainerIDFromCgroupFiles_NilPaths tests the nil-slice edge case.
 func TestExtractContainerIDFromCgroupFiles_NilPaths(t *testing.T) {
+	t.Parallel()
 	id := extractContainerIDFromCgroupFiles(nil)
 	assert.Empty(t, id)
 }
 
 // TestExtractContainerIDFromCgroupFiles_EmptyPaths tests the empty-slice edge case.
 func TestExtractContainerIDFromCgroupFiles_EmptyPaths(t *testing.T) {
+	t.Parallel()
 	id := extractContainerIDFromCgroupFiles([]string{})
 	assert.Empty(t, id)
 }
 
 // TestExtractContainerIDFromCgroupFiles_NonexistentPaths tests that missing files
 // are silently skipped and "" is returned when none exist.
 func TestExtractContainerIDFromCgroupFiles_NonexistentPaths(t *testing.T) {
+	t.Parallel()
 	id := extractContainerIDFromCgroupFiles([]string{"/nonexistent/a", "/nonexistent/b"})
 	assert.Empty(t, id)
 }

internal/sys/container_test.go

@@ -1,6 +1,7 @@
 package sys
 
 import (
+	"bufio"
 	"os"
 	"strings"
 	"testing"
@@ -273,6 +274,8 @@ func TestDetectContainerID_ConsistentWithIsRunningInContainer(t *testing.T) {
 }
 
 func TestExtractContainerIDFromContent(t *testing.T) {
+	t.Parallel()
+
 	tests := []struct {
 		name     string
 		content  string
@@ -348,10 +351,18 @@ func TestExtractContainerIDFromContent(t *testing.T) {
 			content:  "0::/system.slice/docker.service",
 			expected: "",
 		},
+		{
+			// A line that exceeds bufio.MaxScanTokenSize (64 KiB) causes the scanner
+			// to fail with bufio.ErrTooLong. The function logs the error and returns "".
+			name:     "single line exceeding scanner buffer limit returns empty string",
+			content:  strings.Repeat("x", bufio.MaxScanTokenSize+1),
+			expected: "",
+		},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
 			result := extractContainerIDFromContent(tt.content)
 			assert.Equal(t, tt.expected, result)
 		})
@@ -423,6 +434,8 @@ func containsAny(s string, substrings []string) bool {
 }
 
 func TestContainsAny_Helper(t *testing.T) {
+	t.Parallel()
+
 	// Test the helper function itself
 	tests := []struct {
 		name       string
@@ -482,6 +495,7 @@ func TestContainsAny_Helper(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
 			result := containsAny(tt.input, tt.substrings)
 			assert.Equal(t, tt.want, result)
 		})