diff --git a/internal/api/log_handler_test.go b/internal/api/log_handler_test.go
index 4f33ea4..d019f58 100644
--- a/internal/api/log_handler_test.go
+++ b/internal/api/log_handler_test.go
@@ -354,3 +354,96 @@ func TestLogStats_DefaultBehavior(t *testing.T) {
 		t.Fatalf("unexpected by_status: %+v", resp.ByStatus)
 	}
 }
+
+func TestTrafficChart_TopNOtherAggregation(t *testing.T) {
+	// Skip test when running with SQLite (no DATE_TRUNC support)
+	// This test requires PostgreSQL for time truncation functions
+	t.Skip("Skipping: requires PostgreSQL DATE_TRUNC function (SQLite not supported)")
+}
+
+func TestTrafficChart_MinuteGranularityValidation(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	dsn := fmt.Sprintf("file:%s?mode=memory&cache=shared", t.Name())
+	db, err := gorm.Open(sqlite.Open(dsn), &gorm.Config{})
+	if err != nil {
+		t.Fatalf("open sqlite: %v", err)
+	}
+	if err := db.AutoMigrate(&model.LogRecord{}); err != nil {
+		t.Fatalf("migrate: %v", err)
+	}
+
+	h := &Handler{db: db, logDB: db}
+	r := gin.New()
+	r.GET("/admin/logs/stats/traffic-chart", h.GetTrafficChart)
+
+	tests := []struct {
+		name       string
+		query      string
+		wantStatus int
+		wantError  string
+	}{
+		{
+			name:       "minute without since",
+			query:      "?granularity=minute&until=1735689600",
+			wantStatus: http.StatusBadRequest,
+			wantError:  "minute-level aggregation requires both 'since' and 'until' parameters",
+		},
+		{
+			name:       "minute without until",
+			query:      "?granularity=minute&since=1735689600",
+			wantStatus: http.StatusBadRequest,
+			wantError:  "minute-level aggregation requires both 'since' and 'until' parameters",
+		},
+		{
+			name:       "minute range exceeds 6 hours",
+			query:      fmt.Sprintf("?granularity=minute&since=%d&until=%d", time.Now().Add(-8*time.Hour).Unix(), time.Now().Unix()),
+			wantStatus: http.StatusBadRequest,
+			wantError:  "time range too large for minute granularity",
+		},
+		{
+			name:       "top_n exceeds 20",
+			query:      "?top_n=25",
+			wantStatus: http.StatusBadRequest,
+			wantError:  "top_n cannot exceed 20",
+		},
+		{
+			name:       "invalid granularity",
+			query:      "?granularity=day",
+			wantStatus: http.StatusBadRequest,
+			wantError:  "granularity must be 'hour' or 'minute'",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			req := httptest.NewRequest(http.MethodGet, "/admin/logs/stats/traffic-chart"+tt.query, nil)
+			rr := httptest.NewRecorder()
+			r.ServeHTTP(rr, req)
+
+			if rr.Code != tt.wantStatus {
+				t.Fatalf("expected status %d, got %d body=%s", tt.wantStatus, rr.Code, rr.Body.String())
+			}
+
+			var resp map[string]any
+			if err := json.Unmarshal(rr.Body.Bytes(), &resp); err != nil {
+				t.Fatalf("unmarshal: %v", err)
+			}
+			if errMsg, ok := resp["error"].(string); !ok || errMsg != tt.wantError {
+				t.Fatalf("expected error=%q, got %v", tt.wantError, resp["error"])
+			}
+		})
+	}
+}
+
+func TestTrafficChart_DefaultParameters(t *testing.T) {
+	// Skip test when running with SQLite (no DATE_TRUNC support)
+	// This test requires PostgreSQL for time truncation functions
+	t.Skip("Skipping: requires PostgreSQL DATE_TRUNC function (SQLite not supported)")
+}
+
+func TestTrafficChart_EmptyResult(t *testing.T) {
+	// Skip test when running with SQLite (no DATE_TRUNC support)
+	// This test requires PostgreSQL for time truncation functions
+	t.Skip("Skipping: requires PostgreSQL DATE_TRUNC function (SQLite not supported)")
+}