feat: Complete Test Coverage Improvements Feature (#4)

* test: Add comprehensive tests for cmd/node-doctor

Add extensive test coverage for cmd/node-doctor/main.go including:
- Table-driven tests for createMonitors with various scenarios
- NoopExporter tests (ExportStatus, ExportProblem, Stop, concurrent access)
- MonitorFactoryAdapter tests for interface compliance
- DumpConfiguration tests with output validation
- Configuration loading tests with testdata fixtures
- CreateExporters tests with lifecycle management

New testdata fixtures:
- valid_config.yaml: Basic valid configuration
- invalid_syntax.yaml: Malformed YAML for error testing
- empty_monitors.yaml: Edge case with empty monitor list
- full_config.yaml: Complete configuration with all options

Coverage improved from 20.7% to 22.0%. The theoretical maximum for
this package is ~25-30% due to the untestable main() function which
contains signal handling, os.Exit calls, and infinite loops.

Ref: TaskForge #3836

* test: Improve Prometheus exporter test coverage to 93%

Add comprehensive tests for previously uncovered functions:
- TestIsReloadable: Verify interface implementation
- TestReload: Test configuration reload with various scenarios
- TestReloadNotStarted: Test reload on non-started exporter
- TestNeedsServerRestart: Test server restart detection logic
- TestNeedsMetricsRecreation: Test metrics recreation detection
- TestLabelsEqual: Test label comparison edge cases
- TestIsValidMetricName: Test metric name validation
- TestValidateConfig: Test configuration validation
- TestShutdownServer: Test server shutdown scenarios
- TestExportProblemBeforeStart: Test error handling

Add helper function waitForServerReady for robust server
readiness checking instead of time.Sleep.

Improve test reliability with t.Cleanup() for resource
management and proper HTTP client timeouts.

Coverage increased from 63.5% to 93.2%.

* test: Improve pkg/reload test coverage from 68.5% to 93.8%

Add comprehensive tests for configuration validation and file watching:

- Validator tests for all monitor types (kubelet, capacity, log-pattern,
  script, prometheus) with valid configs and error conditions
- Security tests for script path validation (shell metacharacters) and
  file path validation (absolute path requirements)
- Exporter validation tests (Kubernetes, Prometheus, HTTP)
- Remediation and webhook configuration tests
- Watcher tests for empty path handling and default debounce behavior
- Tests for Kubernetes ConfigMap atomic update handling

* test: Improve pkg/detector test coverage from 69.6% to 84.2%

- Fix integration tests by handling both ReloadCoordinator and detector event naming
- Add webhook content comparison in exportersEqual (fixes config change detection bug)
- Add comprehensive statistics tests for GetTotalExports, GetExportSuccessRate, GetDeduplicationRate
- Add MonitorHandle tests for GetConfig, IsRunning, and Stop methods
- Add ProblemDetector.Run() test coverage
- Replace deprecated ioutil functions with os package equivalents
- All tests pass with race detection enabled

Task: #3829

* test: Improve pkg/exporters/kubernetes test coverage from 74.7% to 83.3%

Add comprehensive tests for previously uncovered functions:
- IsReloadable, Reload, needsClientRecreation, annotationsEqual
- performHealthCheck, logMetrics, StatsWithLastError
- ReloadWithClientRecreation
- ConditionUpdate.String
- ConvertConditionsToNodeConditions with status mapping and type prefixing

All tests use table-driven patterns and cover edge cases including
nil inputs, empty collections, and error conditions.

* test: Improve pkg/exporters/http test coverage from 75.6% to 88.3%

Add comprehensive tests for HTTP exporter functionality including:
- IsReloadable and Reload methods with various config scenarios
- needsWorkerPoolRecreation logic for detecting config changes
- performHealthCheck for webhook health monitoring
- min helper function edge cases

Create new stats_test.go with tests for all stats functions:
- RecordDroppedRequest and RecordRetryAttempt tracking
- GetTotalFailures, GetStatusSuccessRate, GetProblemSuccessRate
- WebhookStatsSnapshot GetSuccessRate and IsHealthy methods
- recordRequest with response time averaging
- Thread-safe concurrent access validation

TaskForge: #3831

* test: Improve pkg/monitors/network test coverage from 76.8% to 80.2%

Add comprehensive tests for network monitoring functions:
- TestClassifyHTTPError_NetworkErrors: DNS, dial, and generic network errors
- TestValidateURL: URL validation edge cases
- TestIsValidHTTPMethod: HTTP method validation
- TestGatewayMonitor_getGatewayIP: Gateway IP resolution
- TestParseEndpointConfig_EdgeCases: Endpoint config type validation
- TestNewConnectivityMonitor_EdgeCases: Monitor creation limits
- TestValidateDNSConfig_EdgeCases: DNS config validation
- TestCheckCustomQueries: Custom DNS query handling
- TestParseConnectivityConfig_EdgeCases: Connectivity config parsing

Coverage improvements:
- classifyHTTPError: 57.9% → 89.5%
- validateURL: 60% → 90%
- isValidHTTPMethod: 75% → 100%
- getGatewayIP: 40% → 80%
- checkCustomQueries: 73.3% → 100%
- parseConnectivityConfig: 82.6% → 100%

* test: Improve pkg/types test coverage from 78.1% to 80.3%

Add comprehensive tests for core types package:
- Add ExporterReloadSummary tests (exporter_test.go):
  - TestExporterReloadSummary_AddResult with success/failure scenarios
  - TestExporterReloadResult_Fields for field validation
  - TestExporterReloadSummary_InitialState and order preservation tests

- Add edge case validation tests (types_test.go):
  - TestProblemWithMetadata_NilMetadataMap for nil metadata handling
  - TestConditionValidation_EdgeCases for missing reason/message/transition
  - TestStatusValidation_EdgeCases for missing timestamp/invalid condition
  - TestProblemValidation_EdgeCases for missing severity/message/detected time
  - TestGetMetadata_NilMetadataMap for nil metadata retrieval

Coverage: 78.1% -> 80.3% (exceeds 80% target)
All tests pass with race detection.

* test: Improve pkg/remediators test coverage from 78.1% to 80.4%

Add comprehensive tests for nil logger handling and log methods across
all remediator types:

- base_test.go: Tests for logWarnf/logErrorf with nil and set logger
- network_test.go: Tests for log methods and verifyRoutingTable direct calls
- custom_test.go: Tests for GetScriptPath and log methods
- disk_test.go: Tests for log methods with nil and set logger
- registry_test.go: Tests for log methods with nil and set logger

All tests use proper encapsulation via SetLogger() method calls.

* test: Improve cmd/node-doctor createExporters coverage from 29.8% to 61.7%

Add 9 new test functions for createExporters function:
- TestCreateExporters_HTTPExporterEnabled
- TestCreateExporters_PrometheusExporterEnabled
- TestCreateExporters_HealthServerEnabled
- TestCreateExporters_MultipleExportersEnabled
- TestCreateExporters_HTTPExporterWithValidConfig
- TestCreateExporters_PrometheusWithMetricsPath
- TestCreateExporters_HTTPWithRetryConfig
- TestCreateExporters_HealthServerWithCustomPaths
- TestCreateExporters_ExporterCleanup

Coverage target of 80%+ not achievable due to:
- HTTP exporter success path requires valid kubeconfig/auth config
- Kubernetes exporter requires actual kubeconfig
- Would require integration tests or extensive mocking

Task: #3856

* feat(ci): Add 80% coverage threshold enforcement

- Add coverage-check target to Makefile with 80% threshold
- Add coverage threshold check step to CI workflow for Go 1.25
- Create codecov.yml with project/patch coverage targets (80%)
- Add input validation for missing coverage file and empty results
- Keep Codecov as informational only (inline check is the hard gate)

Task: #3835

Author: mattmattox

.github/workflows/ci.yml

@@ -73,9 +73,35 @@ jobs:
             go tool cover -func=coverage-integration.out | grep total | awk '{print "Integration test coverage: " $3}'
           fi
 
+      - name: Check coverage threshold
+        if: matrix.go-version == '1.25'
+        run: |
+          if [ ! -f coverage.out ]; then
+            echo "::error::Coverage file not found"
+            exit 1
+          fi
+
+          COVERAGE=$(go tool cover -func=coverage.out | grep total | awk '{print $3}' | sed 's/%//')
+
+          if [ -z "$COVERAGE" ]; then
+            echo "::error::Failed to extract coverage percentage"
+            exit 1
+          fi
+
+          THRESHOLD=80
+          echo "Current coverage: ${COVERAGE}%"
+          echo "Minimum threshold: ${THRESHOLD}%"
+
+          if (( $(echo "$COVERAGE < $THRESHOLD" | bc -l) )); then
+            echo "::error::Coverage ${COVERAGE}% is below minimum threshold of ${THRESHOLD}%"
+            exit 1
+          fi
+          echo "Coverage check passed!"
+
       - name: Upload coverage to Codecov
         if: matrix.go-version == '1.25'
         uses: codecov/codecov-action@v4
+        continue-on-error: true  # Codecov is informational; inline check above is the hard gate
         with:
           files: ./coverage.out,./coverage-integration.out
           flags: unittests

Makefile

@@ -23,7 +23,8 @@
 	check-prerequisites check-docker check-kubectl \
 	build test test-integration test-e2e test-all \
 	lint fmt clean install-deps \
-	docker-build docker-push
+	docker-build docker-push \
+	coverage-check
 
 # ================================================================================================
 # Project Configuration
@@ -232,6 +233,20 @@ test-all:
 	@go tool cover -func=coverage/coverage.out | grep total | awk '{print "Total coverage: " $$3}'
 	@$(call print_success,"All tests passed - coverage report: coverage/coverage.html")
 
+# Check coverage meets minimum threshold (80%)
+COVERAGE_THRESHOLD := 80
+coverage-check:
+	@$(call print_status,"Checking coverage threshold (minimum $(COVERAGE_THRESHOLD)%)...")
+	@mkdir -p coverage
+	@go test ./... -covermode=atomic -coverprofile=coverage/coverage.out -short > /dev/null 2>&1
+	@COVERAGE=$$(go tool cover -func=coverage/coverage.out | grep total | awk '{print $$3}' | sed 's/%//'); \
+	echo "Current coverage: $${COVERAGE}%"; \
+	if [ $$(echo "$${COVERAGE} < $(COVERAGE_THRESHOLD)" | bc -l) -eq 1 ]; then \
+		$(call print_error,"Coverage $${COVERAGE}% is below minimum threshold of $(COVERAGE_THRESHOLD)%"); \
+		exit 1; \
+	fi
+	@$(call print_success,"Coverage check passed (>= $(COVERAGE_THRESHOLD)%)")
+
 # Lint code with golangci-lint
 lint:
 	@$(call print_status,"Running golangci-lint...")
@@ -546,6 +561,7 @@ help:
 	@echo "  make test-integration      Run integration tests"
 	@echo "  make test-e2e              Run end-to-end tests"
 	@echo "  make test-all              Run all tests with coverage report"
+	@echo "  make coverage-check        Verify coverage >= 80% threshold"
 	@echo "  make lint                  Run golangci-lint"
 	@echo "  make fmt                   Format code with gofmt and goimports"
 	@echo ""