fix(datamodel): add tests to Copy, make it complain on nil

datamodel/copy.go

@@ -1,6 +1,7 @@
 package datamodel
 
 import (
+	"errors"
 	"fmt"
 )
 
@@ -20,10 +21,13 @@ import (
 // faster shortcuts they might prefer to employ, such as direct struct copying
 // if they share internal memory layouts, etc, have been tried already).
 func Copy(n Node, na NodeAssembler) error {
+	if n == nil {
+		return errors.New("cannot copy a nil node")
+	}
 	switch n.Kind() {
 	case Kind_Null:
 		if n.IsAbsent() {
-			return fmt.Errorf("copying an absent node makes no sense")
+			return errors.New("copying an absent node makes no sense")
 		}
 		return na.AssignNull()
 	case Kind_Bool:

datamodel/copy_test.go

@@ -0,0 +1,92 @@
+package datamodel_test
+
+import (
+	"testing"
+
+	"github.com/ipld/go-ipld-prime/datamodel"
+	"github.com/ipld/go-ipld-prime/fluent/qp"
+	basic "github.com/ipld/go-ipld-prime/node/basicnode"
+)
+
+var copyTests = []struct {
+	name string
+	na   datamodel.NodeBuilder
+	n    datamodel.Node
+	err  string
+}{
+	{name: "Null / Any", na: basic.Prototype.Any.NewBuilder(), n: datamodel.Null},
+	{name: "Int / Any", na: basic.Prototype.Any.NewBuilder(), n: basic.NewInt(100)},
+	{name: "Int / Int", na: basic.Prototype.Int.NewBuilder(), n: basic.NewInt(1000)},
+	{name: "Bool / Any", na: basic.Prototype.Any.NewBuilder(), n: basic.NewBool(true)},
+	{name: "Bool / Bool", na: basic.Prototype.Bool.NewBuilder(), n: basic.NewBool(false)},
+	{name: "Float / Any", na: basic.Prototype.Any.NewBuilder(), n: basic.NewFloat(1.1)},
+	{name: "Float / Float", na: basic.Prototype.Float.NewBuilder(), n: basic.NewFloat(1.2)},
+	{name: "String / Any", na: basic.Prototype.Any.NewBuilder(), n: basic.NewString("mary had")},
+	{name: "String / String", na: basic.Prototype.String.NewBuilder(), n: basic.NewString("a little lamb")},
+	{name: "Bytes / Any", na: basic.Prototype.Any.NewBuilder(), n: basic.NewBytes([]byte("mary had"))},
+	{name: "Bytes / Bytes", na: basic.Prototype.Bytes.NewBuilder(), n: basic.NewBytes([]byte("a little lamb"))},
+	{name: "Link / Any", na: basic.Prototype.Any.NewBuilder(), n: basic.NewLink(globalLink)},
+	{name: "Link / Link", na: basic.Prototype.Link.NewBuilder(), n: basic.NewLink(globalLink2)},
+	{
+		name: "List / Any",
+		na:   basic.Prototype.Any.NewBuilder(),
+		n: qpMust(qp.BuildList(basic.Prototype.Any, -1, func(am datamodel.ListAssembler) {
+			qp.ListEntry(am, qp.Int(7))
+			qp.ListEntry(am, qp.Int(8))
+		})),
+	},
+	{
+		name: "List / List",
+		na:   basic.Prototype.List.NewBuilder(),
+		n: qpMust(qp.BuildList(basic.Prototype.List, -1, func(am datamodel.ListAssembler) {
+			qp.ListEntry(am, qp.String("yep"))
+			qp.ListEntry(am, qp.Int(8))
+			qp.ListEntry(am, qp.String("nope"))
+		})),
+	},
+	{
+		name: "Map / Any",
+		na:   basic.Prototype.Any.NewBuilder(),
+		n: qpMust(qp.BuildMap(basic.Prototype.Any, -1, func(am datamodel.MapAssembler) {
+			qp.MapEntry(am, "foo", qp.Int(7))
+			qp.MapEntry(am, "bar", qp.Int(8))
+		})),
+	},
+	{
+		name: "Map / Map",
+		na:   basic.Prototype.Map.NewBuilder(),
+		n: qpMust(qp.BuildMap(basic.Prototype.Map, -1, func(am datamodel.MapAssembler) {
+			qp.MapEntry(am, "foo", qp.Int(7))
+			qp.MapEntry(am, "bar", qp.Int(8))
+			qp.MapEntry(am, "bang", qp.Link(globalLink))
+		})),
+	},
+	{name: "nil", na: basic.Prototype.Any.NewBuilder(), n: nil, err: "cannot copy a nil node"},
+	{name: "absent", na: basic.Prototype.Any.NewBuilder(), n: datamodel.Absent, err: "copying an absent node makes no sense"},
+}
+
+func TestCopy(t *testing.T) {
+	for _, tt := range copyTests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			err := datamodel.Copy(tt.n, tt.na)
+			if err != nil {
+				if tt.err != "" {
+					if err.Error() != tt.err {
+						t.Fatalf("expected error %q, got %q", tt.err, err.Error())
+					}
+				} else {
+					t.Fatal(err)
+				}
+				return
+			} else if tt.err != "" {
+				t.Fatalf("expected error %q, got nil", tt.err)
+				return
+			}
+			out := tt.na.Build()
+			if !datamodel.DeepEqual(tt.n, out) {
+				t.Fatalf("deep equal failed")
+			}
+		})
+	}
+}