graph/encoding: provide attribute handling out of the box

graph/encoding/encoding_test.go

@@ -0,0 +1,121 @@
+// Copyright ©2021 The Gonum Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package encoding
+
+import (
+	"sort"
+	"testing"
+)
+
+var setAttributesTests = []struct {
+	attr   *Attributes
+	opName string
+	op     func(AttributeSetter) error
+	want   *Attributes
+}{
+	{
+		attr:   &Attributes{},
+		opName: "noop",
+		op: func(a AttributeSetter) error {
+			return a.SetAttribute(Attribute{Key: "", Value: "bar"})
+		},
+		want: &Attributes{},
+	},
+	{
+		attr:   &Attributes{},
+		opName: "add attr to empty",
+		op: func(a AttributeSetter) error {
+			return a.SetAttribute(Attribute{Key: "foo", Value: "bar"})
+		},
+		want: &Attributes{{Key: "foo", Value: "bar"}},
+	},
+	{
+		attr:   &Attributes{},
+		opName: "remove attr from empty",
+		op: func(a AttributeSetter) error {
+			return a.SetAttribute(Attribute{Key: "foo", Value: ""})
+		},
+		want: &Attributes{},
+	},
+	{
+		attr:   &Attributes{{Key: "foo", Value: "bar"}},
+		opName: "add attr to non-empty",
+		op: func(a AttributeSetter) error {
+			return a.SetAttribute(Attribute{Key: "bif", Value: "fud"})
+		},
+		want: &Attributes{{Key: "foo", Value: "bar"}, {Key: "bif", Value: "fud"}},
+	},
+	{
+		attr:   &Attributes{{Key: "foo", Value: "bar"}},
+		opName: "remove attr from singleton",
+		op: func(a AttributeSetter) error {
+			return a.SetAttribute(Attribute{Key: "foo", Value: ""})
+		},
+		want: &Attributes{},
+	},
+	{
+		attr:   &Attributes{{Key: "foo", Value: "bar"}, {Key: "bif", Value: "fud"}},
+		opName: "remove first attr from pair",
+		op: func(a AttributeSetter) error {
+			return a.SetAttribute(Attribute{Key: "foo", Value: ""})
+		},
+		want: &Attributes{{Key: "bif", Value: "fud"}},
+	},
+	{
+		attr:   &Attributes{{Key: "foo", Value: "bar"}, {Key: "bif", Value: "fud"}},
+		opName: "remove second attr from pair",
+		op: func(a AttributeSetter) error {
+			return a.SetAttribute(Attribute{Key: "bif", Value: ""})
+		},
+		want: &Attributes{{Key: "foo", Value: "bar"}},
+	},
+	{
+		attr:   &Attributes{{Key: "foo", Value: "bar"}, {Key: "bif", Value: "fud"}},
+		opName: "replace first attr in pair",
+		op: func(a AttributeSetter) error {
+			return a.SetAttribute(Attribute{Key: "foo", Value: "not bar"})
+		},
+		want: &Attributes{{Key: "foo", Value: "not bar"}, {Key: "bif", Value: "fud"}},
+	},
+	{
+		attr:   &Attributes{{Key: "foo", Value: "bar"}, {Key: "bif", Value: "fud"}},
+		opName: "replace second attr in pair",
+		op: func(a AttributeSetter) error {
+			return a.SetAttribute(Attribute{Key: "bif", Value: "not fud"})
+		},
+		want: &Attributes{{Key: "foo", Value: "bar"}, {Key: "bif", Value: "not fud"}},
+	},
+}
+
+func TestSetAttributes(t *testing.T) {
+	for _, test := range setAttributesTests {
+		err := test.op(test.attr)
+		if err != nil {
+			t.Errorf("unexpected error for %q: %v", test.opName, err)
+			continue
+		}
+		if !sameAttributes(test.attr, test.want) {
+			t.Errorf("unexpected result from %q:\ngot: %+v\nwant:%+v", test.opName, test.attr, test.want)
+		}
+	}
+}
+
+func sameAttributes(a, b Attributer) bool {
+	aAttr := a.Attributes()
+	bAttr := b.Attributes()
+	if len(aAttr) != len(bAttr) {
+		return false
+	}
+	aAttr = append(aAttr[:0:0], aAttr...)
+	sort.Slice(aAttr, func(i, j int) bool { return aAttr[i].Key < aAttr[j].Key })
+	bAttr = append(bAttr[:0:0], bAttr...)
+	sort.Slice(bAttr, func(i, j int) bool { return bAttr[i].Key < bAttr[j].Key })
+	for i, a := range aAttr {
+		if bAttr[i] != a {
+			return false
+		}
+	}
+	return true
+}