add initial test

v2/pkg/engine/plan/interface_selection_rewriter_test.go

@@ -0,0 +1,99 @@
+package plan
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/wundergraph/graphql-go-tools/v2/internal/pkg/unsafeparser"
+	"github.com/wundergraph/graphql-go-tools/v2/internal/pkg/unsafeprinter"
+	"github.com/wundergraph/graphql-go-tools/v2/pkg/ast"
+)
+
+func TestInterfaceSelectionRewriter_RewriteOperation(t *testing.T) {
+	run := func(t *testing.T, definition string, dsConfiguration *DataSourceConfiguration, operation string, expectedOperation string) {
+		t.Helper()
+
+		op := unsafeparser.ParseGraphqlDocumentString(operation)
+		def := unsafeparser.ParseGraphqlDocumentStringWithBaseSchema(definition)
+
+		fieldRef := ast.InvalidRef
+		for ref, _ := range op.Fields {
+			if op.FieldNameString(ref) == "iface" {
+				fieldRef = ref
+				break
+			}
+		}
+
+		node, _ := def.Index.FirstNodeByNameStr("Query")
+
+		rewriter := newInterfaceSelectionRewriter(&op, &def)
+		rewriter.RewriteOperation(fieldRef, node, dsConfiguration)
+
+		printedOp := unsafeprinter.PrettyPrint(&op, &def)
+		expectedPretty := unsafeprinter.Prettify(expectedOperation)
+
+		require.Equal(t, expectedPretty, printedOp)
+	}
+
+	t.Run("simple", func(t *testing.T) {
+		definition := `
+			interface Node {
+				id: ID!
+				name: String!
+			}
+			
+			type User implements Node {
+				id: ID!
+				name: String!
+			}
+
+			type Admin implements Node {
+				id: ID!
+				name: String! @external
+			}
+			
+			type Query {
+				iface: Node!
+			}
+		`
+
+		operation := `
+			query {
+				iface {
+					name
+				}
+			}`
+
+		expectedOperation := `
+			query {
+				iface {
+					... on User {
+						name
+					}
+					... on Admin {
+						name
+					}
+				}
+			}
+		`
+
+		dsConfiguration := dsb().
+			RootNode("Query", "iface").
+			RootNode("User", "id", "name").
+			RootNode("Admin", "id").ds
+
+		dsConfiguration.FederationMetaData.Keys = FederationFieldConfigurations{
+			{
+				TypeName:     "User",
+				SelectionSet: "id",
+			},
+			{
+				TypeName:     "Admin",
+				SelectionSet: "id",
+			},
+		}
+
+		run(t, definition, dsConfiguration, operation, expectedOperation)
+	})
+}