history plot

main_test.go

@@ -81,3 +81,31 @@ func TestLoadConfig(t *testing.T) {
 		t.Fatalf("addr = %q, want %q", cfg.Addr, ":9090")
 	}
 }
+
+func TestBuildHistoryChartEmpty(t *testing.T) {
+	chart := buildHistoryChart(nil)
+	if !strings.Contains(string(chart), "No power history yet") {
+		t.Fatalf("empty chart did not contain fallback text: %s", string(chart))
+	}
+}
+
+func TestBuildHistoryChartRendersPolyline(t *testing.T) {
+	history := []sample{
+		{at: time.Date(2026, 4, 20, 0, 0, 0, 0, time.UTC), value: 100},
+		{at: time.Date(2026, 4, 20, 6, 0, 0, 0, time.UTC), value: 200},
+		{at: time.Date(2026, 4, 20, 12, 0, 0, 0, time.UTC), value: 150},
+	}
+
+	chart := buildHistoryChart(history)
+	if !strings.Contains(string(chart), "<polyline") {
+		t.Fatalf("chart did not contain polyline: %s", string(chart))
+	}
+	for _, want := range []string{"W", "00:00", "06:00", "12:00"} {
+		if !strings.Contains(string(chart), want) {
+			t.Fatalf("chart did not include %q: %s", want, string(chart))
+		}
+	}
+	if !strings.Contains(string(chart), "0 W") {
+		t.Fatalf("chart did not include zero baseline: %s", string(chart))
+	}
+}