Go Test Coverage

Test coverage gap analysis and recommendations for Go projects. Identifies missing or insufficient test coverage and generates actionable recommendations.

What It Does

1. Coverage Analysis — Runs go test -cover and parses results
2. Gap Identification — Finds untested exported functions, error paths, and edge cases
3. Recommendation Engine — Suggests specific test cases using table-driven patterns
4. Stub Generation — Creates ready-to-use test file stubs

Steps

API Integration (Optional)

If GOPHER_GUIDES_API_KEY is set, verify it:

curl -s -H "Authorization: Bearer $GOPHER_GUIDES_API_KEY" \
  https://gopherguides.com/api/gopher-ai/me

If not set, local analysis tools (go vet, staticcheck, golangci-lint) still provide comprehensive analysis. Set the key for enhanced API-powered insights. Get your key at gopherguides.com.

1. Measure Current Coverage

# Generate coverage profile
go test -coverprofile=coverage.out ./...

# View per-function coverage
go tool cover -func=coverage.out

# Generate HTML report (optional)
go tool cover -html=coverage.out -o coverage.html

2. Identify Gaps

Parse coverage output to find:

• Untested exported functions — Any func with 0% coverage
• Partially covered functions — Functions with branches not hit
• Untested error paths — if err != nil blocks never executed
• Missing edge cases — Boundary conditions not exercised

# Find functions with 0% coverage
go tool cover -func=coverage.out | grep "0.0%"

# Find exported functions without test files
for f in $(find . -name "*.go" ! -name "*_test.go" -path "*/pkg/*" -o -name "*.go" ! -name "*_test.go" -path "*/internal/*"); do
  dir=$(dirname "$f")
  base=$(basename "$f" .go)
  if [ ! -f "${dir}/${base}_test.go" ]; then
    echo "Missing test file: ${dir}/${base}_test.go"
  fi
done

3. Generate Recommendations

For each untested function, recommend:

• Table-driven tests for functions with multiple input/output combinations
• Error path tests for functions that return errors
• Edge case tests for boundary values (nil, empty, zero, max)
• Integration tests for functions with external dependencies

4. Generate Test Stubs

Create test files with the table-driven pattern:

func TestFunctionName(t *testing.T) {
	tests := []struct {
		name    string
		input   InputType
		want    OutputType
		wantErr bool
	}{
		{
			name:  "valid input",
			input: validInput,
			want:  expectedOutput,
		},
		{
			name:    "empty input returns error",
			input:   emptyInput,
			wantErr: true,
		},
		{
			name:    "nil input returns error",
			input:   nil,
			wantErr: true,
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()
			got, err := FunctionName(tt.input)
			if (err != nil) != tt.wantErr {
				t.Errorf("FunctionName() error = %v, wantErr %v", err, tt.wantErr)
				return
			}
			if !reflect.DeepEqual(got, tt.want) {
				t.Errorf("FunctionName() = %v, want %v", got, tt.want)
			}
		})
	}
}

Output Format

## Test Coverage Report

**Project:** {name}
**Current Coverage:** {percent}%
**Target Coverage:** 80%

### Coverage by Package

| Package | Coverage | Status |
|---------|----------|--------|
| pkg/auth | 85% | ✅ |
| pkg/api | 45% | ⚠️ |
| internal/db | 20% | 🔴 |

### Untested Exported Functions

| Function | File | Priority |
|----------|------|----------|
| `HandleLogin` | pkg/auth/handler.go | High |
| `ValidateToken` | pkg/auth/token.go | High |
| `FormatResponse` | pkg/api/response.go | Medium |

### Recommended Test Cases

#### `HandleLogin` (pkg/auth/handler.go)
1. Valid credentials → successful login
2. Invalid password → 401 error
3. Missing username → validation error
4. Expired account → forbidden error
5. Rate limited → 429 error

### Generated Stubs

Test stubs have been written to:
- `pkg/auth/handler_test.go`
- `pkg/api/response_test.go`

Helper Script

After installation via install.sh, scripts are at .github/skills/scripts/. Run the coverage report script for a formatted summary with gap analysis:

bash .github/skills/scripts/coverage-report.sh [minimum-coverage-percent]

Default minimum is 80%. Configure thresholds in severity configuration at the installed path:

coverage:
  minimum: 80
  per_package_minimum: 60
  below_threshold_severity: warning

Gopher Guides API Integration

Note: API calls send source code to gopherguides.com for analysis. Ensure your organization's policy permits external code analysis.

For full API usage examples, see API Usage Reference.

References

• Existing gopher-ai command: plugins/go-dev/commands/test-gen.md
• Go best practices skill: plugins/go-dev/skills/go-best-practices/
• Go Testing

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