test + docs: close 12 test gaps (~250 new tests) and expand testing guide to 34 parts

Implements all P0-P2 test gaps from docs/test-gap-prompt.md:
- Deployment service tests (20), target service tests (18), scheduler tests (8)
- Agent binary tests (48), CSR renewal tests (8), short-lived cert tests (7)
- Domain model tests (25), context cancellation tests (9), concurrency tests (7)
- Handler negative-path tests (23 across 5 files)
- Frontend error handling tests (86) and API client tests (7)

Expands testing-guide.md from 28 to 34 parts covering certificate export,
S/MIME/EKU, OCSP/DER CRL, body size limits, Apache/HAProxy connectors,
and sub-CA mode. Fixes stale profile count (4->5) and updates sign-off table.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/api/handler/discovery_handler_test.go

@@ -610,3 +610,122 @@ func TestGetDiscoverySummary_MethodNotAllowed(t *testing.T) {
 		t.Errorf("expected status %d, got %d", http.StatusMethodNotAllowed, w.Code)
 	}
 }
+
+// Test DismissDiscovered - service error
+func TestDismissDiscovered_ServiceError(t *testing.T) {
+	mock := &MockDiscoveryService{
+		DismissDiscoveredFn: func(ctx context.Context, id string) error {
+			return fmt.Errorf("database error")
+		},
+	}
+
+	handler := NewDiscoveryHandler(mock)
+
+	req := httptest.NewRequest(http.MethodPost, "/api/v1/discovered-certificates/dcert-1/dismiss", nil)
+	req = req.WithContext(discoveryContextWithRequestID())
+	req.SetPathValue("id", "dcert-1")
+	w := httptest.NewRecorder()
+
+	handler.DismissDiscovered(w, req)
+
+	if w.Code != http.StatusInternalServerError {
+		t.Errorf("expected status %d, got %d", http.StatusInternalServerError, w.Code)
+	}
+}
+
+// Test ClaimDiscovered - invalid body (malformed JSON)
+func TestClaimDiscovered_InvalidJSON(t *testing.T) {
+	mock := &MockDiscoveryService{}
+	handler := NewDiscoveryHandler(mock)
+
+	req := httptest.NewRequest(http.MethodPost, "/api/v1/discovered-certificates/dcert-1/claim", bytes.NewReader([]byte("invalid json")))
+	req = req.WithContext(discoveryContextWithRequestID())
+	req.SetPathValue("id", "dcert-1")
+	w := httptest.NewRecorder()
+
+	handler.ClaimDiscovered(w, req)
+
+	if w.Code != http.StatusBadRequest {
+		t.Errorf("expected status %d, got %d", http.StatusBadRequest, w.Code)
+	}
+}
+
+// Test ClaimDiscovered - method not allowed
+func TestClaimDiscovered_MethodNotAllowed(t *testing.T) {
+	mock := &MockDiscoveryService{}
+	handler := NewDiscoveryHandler(mock)
+
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/discovered-certificates/dcert-1/claim", nil)
+	req = req.WithContext(discoveryContextWithRequestID())
+	req.SetPathValue("id", "dcert-1")
+	w := httptest.NewRecorder()
+
+	handler.ClaimDiscovered(w, req)
+
+	if w.Code != http.StatusMethodNotAllowed {
+		t.Errorf("expected status %d, got %d", http.StatusMethodNotAllowed, w.Code)
+	}
+}
+
+// Test ListDiscovered - service error
+func TestListDiscovered_ServiceError(t *testing.T) {
+	mock := &MockDiscoveryService{
+		ListDiscoveredFn: func(ctx context.Context, agentID, status string, page, perPage int) ([]*domain.DiscoveredCertificate, int, error) {
+			return nil, 0, fmt.Errorf("database error")
+		},
+	}
+
+	handler := NewDiscoveryHandler(mock)
+
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/discovered-certificates", nil)
+	req = req.WithContext(discoveryContextWithRequestID())
+	w := httptest.NewRecorder()
+
+	handler.ListDiscovered(w, req)
+
+	if w.Code != http.StatusInternalServerError {
+		t.Errorf("expected status %d, got %d", http.StatusInternalServerError, w.Code)
+	}
+}
+
+// Test ListScans - service error
+func TestListScans_ServiceError(t *testing.T) {
+	mock := &MockDiscoveryService{
+		ListScansFn: func(ctx context.Context, agentID string, page, perPage int) ([]*domain.DiscoveryScan, int, error) {
+			return nil, 0, fmt.Errorf("database error")
+		},
+	}
+
+	handler := NewDiscoveryHandler(mock)
+
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/discovery-scans", nil)
+	req = req.WithContext(discoveryContextWithRequestID())
+	w := httptest.NewRecorder()
+
+	handler.ListScans(w, req)
+
+	if w.Code != http.StatusInternalServerError {
+		t.Errorf("expected status %d, got %d", http.StatusInternalServerError, w.Code)
+	}
+}
+
+// Test GetDiscoverySummary - service error
+func TestGetDiscoverySummary_ServiceError(t *testing.T) {
+	mock := &MockDiscoveryService{
+		GetDiscoverySummaryFn: func(ctx context.Context) (map[string]int, error) {
+			return nil, fmt.Errorf("database error")
+		},
+	}
+
+	handler := NewDiscoveryHandler(mock)
+
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/discovery-summary", nil)
+	req = req.WithContext(discoveryContextWithRequestID())
+	w := httptest.NewRecorder()
+
+	handler.GetDiscoverySummary(w, req)
+
+	if w.Code != http.StatusInternalServerError {
+		t.Errorf("expected status %d, got %d", http.StatusInternalServerError, w.Code)
+	}
+}

internal/api/handler/est_handler_test.go

@@ -396,3 +396,49 @@ func TestASN1EncodeLength(t *testing.T) {
 		}
 	}
 }
+
+func TestESTCSRAttrs_ServiceError(t *testing.T) {
+	svc := &mockESTService{
+		CSRAttrsErr: errors.New("service error"),
+	}
+	h := NewESTHandler(svc)
+
+	req := httptest.NewRequest(http.MethodGet, "/.well-known/est/csrattrs", nil)
+	w := httptest.NewRecorder()
+	h.CSRAttrs(w, req)
+
+	if w.Code != http.StatusInternalServerError {
+		t.Errorf("expected 500, got %d", w.Code)
+	}
+}
+
+func TestESTSimpleReEnroll_ServiceError(t *testing.T) {
+	csrPEM := generateTestCSRPEM(t)
+	svc := &mockESTService{
+		EnrollErr: errors.New("renewal failed"),
+	}
+	h := NewESTHandler(svc)
+
+	req := httptest.NewRequest(http.MethodPost, "/.well-known/est/simplereenroll", strings.NewReader(csrPEM))
+	w := httptest.NewRecorder()
+	h.SimpleReEnroll(w, req)
+
+	if w.Code != http.StatusInternalServerError {
+		t.Errorf("expected 500, got %d", w.Code)
+	}
+}
+
+func TestESTCACerts_UnableToGetCerts(t *testing.T) {
+	svc := &mockESTService{
+		CACertErr: errors.New("CA unavailable"),
+	}
+	h := NewESTHandler(svc)
+
+	req := httptest.NewRequest(http.MethodGet, "/.well-known/est/cacerts", nil)
+	w := httptest.NewRecorder()
+	h.CACerts(w, req)
+
+	if w.Code != http.StatusInternalServerError {
+		t.Errorf("expected 500, got %d", w.Code)
+	}
+}

internal/api/handler/export_handler_test.go

@@ -12,6 +12,8 @@ import (
 	"github.com/shankar0123/certctl/internal/service"
 )
 
+// Add context import was already there — verify import is present above
+
 // MockExportService is a mock implementation of ExportService interface.
 type MockExportService struct {
 	ExportPEMFn    func(ctx context.Context, certID string) (*service.ExportPEMResult, error)
@@ -280,3 +282,38 @@ func TestExtractCertIDFromExportPath(t *testing.T) {
 		}
 	}
 }
+
+func TestExportPKCS12_InvalidJSON(t *testing.T) {
+	mockSvc := &MockExportService{
+		ExportPKCS12Fn: func(_ context.Context, _ string, password string) ([]byte, error) {
+			// Invalid JSON is silently ignored, defaults to empty password
+			if password != "" {
+				t.Errorf("expected empty password (invalid JSON ignored), got %s", password)
+			}
+			return []byte{0x30}, nil
+		},
+	}
+	h := NewExportHandler(mockSvc)
+
+	req := httptest.NewRequest(http.MethodPost, "/api/v1/certificates/mc-test-1/export/pkcs12", strings.NewReader(`{"invalid json`))
+	w := httptest.NewRecorder()
+
+	h.ExportPKCS12(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("expected 200 (invalid JSON ignored), got %d", w.Code)
+	}
+}
+
+func TestExportPEM_MethodNotAllowedDelete(t *testing.T) {
+	h := NewExportHandler(&MockExportService{})
+
+	req := httptest.NewRequest(http.MethodDelete, "/api/v1/certificates/mc-test-1/export/pem", nil)
+	w := httptest.NewRecorder()
+
+	h.ExportPEM(w, req)
+
+	if w.Code != http.StatusMethodNotAllowed {
+		t.Fatalf("expected 405, got %d", w.Code)
+	}
+}

internal/api/handler/stats_handler_test.go

@@ -316,3 +316,115 @@ func TestGetPrometheusMetrics_ZeroValues(t *testing.T) {
 func containsLine(text, substr string) bool {
 	return strings.Contains(text, substr)
 }
+
+// Test GetCertificatesByStatus - method not allowed
+func TestGetCertificatesByStatus_MethodNotAllowed(t *testing.T) {
+	mock := &MockStatsService{}
+	h := NewStatsHandler(mock)
+	req := httptest.NewRequest(http.MethodPost, "/api/v1/stats/certificates-by-status", nil)
+	w := httptest.NewRecorder()
+	h.GetCertificatesByStatus(w, req)
+	if w.Code != http.StatusMethodNotAllowed {
+		t.Errorf("expected 405, got %d", w.Code)
+	}
+}
+
+// Test GetCertificatesByStatus - service error
+func TestGetCertificatesByStatus_ServiceError(t *testing.T) {
+	mock := &MockStatsService{
+		GetCertificatesByStatusFn: func(ctx context.Context) (interface{}, error) {
+			return nil, fmt.Errorf("db error")
+		},
+	}
+	h := NewStatsHandler(mock)
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/stats/certificates-by-status", nil)
+	w := httptest.NewRecorder()
+	h.GetCertificatesByStatus(w, req)
+	if w.Code != http.StatusInternalServerError {
+		t.Errorf("expected 500, got %d", w.Code)
+	}
+}
+
+// Test GetExpirationTimeline - method not allowed
+func TestGetExpirationTimeline_MethodNotAllowed(t *testing.T) {
+	mock := &MockStatsService{}
+	h := NewStatsHandler(mock)
+	req := httptest.NewRequest(http.MethodPost, "/api/v1/stats/expiration-timeline", nil)
+	w := httptest.NewRecorder()
+	h.GetExpirationTimeline(w, req)
+	if w.Code != http.StatusMethodNotAllowed {
+		t.Errorf("expected 405, got %d", w.Code)
+	}
+}
+
+// Test GetExpirationTimeline - service error
+func TestGetExpirationTimeline_ServiceError(t *testing.T) {
+	mock := &MockStatsService{
+		GetExpirationTimelineFn: func(ctx context.Context, days int) (interface{}, error) {
+			return nil, fmt.Errorf("db error")
+		},
+	}
+	h := NewStatsHandler(mock)
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/stats/expiration-timeline?days=30", nil)
+	w := httptest.NewRecorder()
+	h.GetExpirationTimeline(w, req)
+	if w.Code != http.StatusInternalServerError {
+		t.Errorf("expected 500, got %d", w.Code)
+	}
+}
+
+// Test GetJobTrends - method not allowed
+func TestGetJobTrends_MethodNotAllowed(t *testing.T) {
+	mock := &MockStatsService{}
+	h := NewStatsHandler(mock)
+	req := httptest.NewRequest(http.MethodPost, "/api/v1/stats/job-trends", nil)
+	w := httptest.NewRecorder()
+	h.GetJobTrends(w, req)
+	if w.Code != http.StatusMethodNotAllowed {
+		t.Errorf("expected 405, got %d", w.Code)
+	}
+}
+
+// Test GetJobTrends - service error
+func TestGetJobTrends_ServiceError(t *testing.T) {
+	mock := &MockStatsService{
+		GetJobStatsFn: func(ctx context.Context, days int) (interface{}, error) {
+			return nil, fmt.Errorf("db error")
+		},
+	}
+	h := NewStatsHandler(mock)
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/stats/job-trends?days=14", nil)
+	w := httptest.NewRecorder()
+	h.GetJobTrends(w, req)
+	if w.Code != http.StatusInternalServerError {
+		t.Errorf("expected 500, got %d", w.Code)
+	}
+}
+
+// Test GetIssuanceRate - method not allowed
+func TestGetIssuanceRate_MethodNotAllowed(t *testing.T) {
+	mock := &MockStatsService{}
+	h := NewStatsHandler(mock)
+	req := httptest.NewRequest(http.MethodPost, "/api/v1/stats/issuance-rate", nil)
+	w := httptest.NewRecorder()
+	h.GetIssuanceRate(w, req)
+	if w.Code != http.StatusMethodNotAllowed {
+		t.Errorf("expected 405, got %d", w.Code)
+	}
+}
+
+// Test GetIssuanceRate - service error
+func TestGetIssuanceRate_ServiceError(t *testing.T) {
+	mock := &MockStatsService{
+		GetIssuanceRateFn: func(ctx context.Context, days int) (interface{}, error) {
+			return nil, fmt.Errorf("db error")
+		},
+	}
+	h := NewStatsHandler(mock)
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/stats/issuance-rate?days=7", nil)
+	w := httptest.NewRecorder()
+	h.GetIssuanceRate(w, req)
+	if w.Code != http.StatusInternalServerError {
+		t.Errorf("expected 500, got %d", w.Code)
+	}
+}

internal/api/handler/verification_handler_test.go

@@ -249,6 +249,58 @@ func TestVerifyDeployment_ServiceError(t *testing.T) {
 	}
 }
 
+func TestVerifyDeployment_EmptyBody(t *testing.T) {
+	mockSvc := &mockVerificationService{}
+	handler := NewVerificationHandler(mockSvc)
+
+	httpReq := httptest.NewRequest("POST", "/api/v1/jobs/j-test10/verify", bytes.NewBufferString(""))
+	w := httptest.NewRecorder()
+
+	handler.VerifyDeployment(w, httpReq)
+
+	if w.Code != http.StatusBadRequest {
+		t.Errorf("expected status 400, got %d", w.Code)
+	}
+}
+
+func TestGetVerificationStatus_ServiceError(t *testing.T) {
+	mockSvc := &mockVerificationService{
+		getErr: ErrServiceUnavailable,
+	}
+	handler := NewVerificationHandler(mockSvc)
+
+	httpReq := httptest.NewRequest("GET", "/api/v1/jobs/j-test11/verification", nil)
+	w := httptest.NewRecorder()
+
+	handler.GetVerificationStatus(w, httpReq)
+
+	if w.Code != http.StatusInternalServerError {
+		t.Errorf("expected status 500, got %d", w.Code)
+	}
+}
+
+func TestGetVerificationStatus_NotFound(t *testing.T) {
+	mockSvc := &mockVerificationService{
+		results: make(map[string]*domain.VerificationResult),
+	}
+	handler := NewVerificationHandler(mockSvc)
+
+	httpReq := httptest.NewRequest("GET", "/api/v1/jobs/j-nonexistent/verification", nil)
+	w := httptest.NewRecorder()
+
+	handler.GetVerificationStatus(w, httpReq)
+
+	if w.Code != http.StatusOK {
+		t.Errorf("expected status 200, got %d", w.Code)
+	}
+
+	var result *domain.VerificationResult
+	json.NewDecoder(w.Body).Decode(&result)
+	if result != nil {
+		t.Error("expected nil result for nonexistent job")
+	}
+}
+
 var ErrServiceUnavailable = NewServiceError("service unavailable")
 
 func NewServiceError(msg string) error {