layout: add test that Flex doesn't allocate

Signed-off-by: Elias Naur <mail@eliasnaur.com>

layout/layout_test.go

@@ -0,0 +1,67 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package layout
+
+import (
+	"image"
+	"testing"
+
+	"gioui.org/op"
+)
+
+func TestStack(t *testing.T) {
+	gtx := Context{
+		Ops: new(op.Ops),
+		Constraints: Constraints{
+			Max: image.Pt(100, 100),
+		},
+	}
+	exp := image.Point{X: 60, Y: 70}
+	dims := Stack{Alignment: Center}.Layout(gtx,
+		Expanded(func(gtx Context) Dimensions {
+			return Dimensions{Size: exp}
+		}),
+		Stacked(func(gtx Context) Dimensions {
+			return Dimensions{Size: image.Point{X: 50, Y: 50}}
+		}),
+	)
+	if got := dims.Size; got != exp {
+		t.Errorf("Stack ignored Expanded size, got %v expected %v", got, exp)
+	}
+}
+
+func TestStackAllocs(t *testing.T) {
+	var ops op.Ops
+	allocs := testing.AllocsPerRun(1, func() {
+		ops.Reset()
+		gtx := Context{
+			Ops: &ops,
+		}
+		Stack{}.Layout(gtx,
+			Stacked(func(gtx Context) Dimensions {
+				return Dimensions{Size: image.Point{X: 50, Y: 50}}
+			}),
+		)
+	})
+	if allocs != 0 {
+		t.Errorf("expected no allocs, got %f", allocs)
+	}
+}
+
+func TestFlexAllocs(t *testing.T) {
+	var ops op.Ops
+	allocs := testing.AllocsPerRun(1, func() {
+		ops.Reset()
+		gtx := Context{
+			Ops: &ops,
+		}
+		Flex{}.Layout(gtx,
+			Rigid(func(gtx Context) Dimensions {
+				return Dimensions{Size: image.Point{X: 50, Y: 50}}
+			}),
+		)
+	})
+	if allocs != 0 {
+		t.Errorf("expected no allocs, got %f", allocs)
+	}
+}