Cover the loss window, rate window, error taxonomy and formatters with tests

ui_test.go

@@ -0,0 +1,28 @@
+package main
+
+import "testing"
+
+func TestGridCellFullRow(t *testing.T) {
+	x0, w0 := gridCell(0, 2, 0, 100)
+	x1, w1 := gridCell(1, 2, 0, 100)
+	if w0 != w1 {
+		t.Errorf("cells differ in width: %d vs %d", w0, w1)
+	}
+	if x0 != 0 {
+		t.Errorf("first cell x = %d, want 0", x0)
+	}
+	if x1+w1 != 100 {
+		t.Errorf("row ends at %d, want 100", x1+w1)
+	}
+	if got := x1 - (x0 + w0); got != chipGap {
+		t.Errorf("gap between cells = %d, want %d", got, chipGap)
+	}
+}
+
+// A last row that does not fill the grid is centred.
+func TestGridCellShortLastRow(t *testing.T) {
+	cx, cw := gridCell(2, 3, 0, 100)
+	if left, right := cx, 100-(cx+cw); left != right {
+		t.Errorf("lone cell has %d left and %d right, want centred", left, right)
+	}
+}