schema: move 'concurrent schema update' error to constants

Closes #TNTP-3336

Author: bigbes

schema.go

@@ -19,6 +19,10 @@ const (
 	vspaceSpFormatFieldNum = 7
 )
 
+var (
+	ErrConcurrentSchemaUpdate = errors.New("concurrent schema update")
+)
+
 func msgpackIsUint(code byte) bool {
 	return code == msgpcode.Uint8 || code == msgpcode.Uint16 ||
 		code == msgpcode.Uint32 || code == msgpcode.Uint64 ||
@@ -415,7 +419,7 @@ func GetSchema(doer Doer) (Schema, error) {
 			schema.SpacesById[spaceId].IndexesById[index.Id] = index
 			schema.SpacesById[spaceId].Indexes[index.Name] = index
 		} else {
-			return Schema{}, errors.New("concurrent schema update")
+			return Schema{}, ErrConcurrentSchemaUpdate
 		}
 	}
 

tarantool_test.go

@@ -3999,14 +3999,13 @@ func TestConnect_schema_update(t *testing.T) {
 	for i := 0; i < 100; i++ {
 		fut := conn.Do(NewCallRequest("create_spaces"))
 
-		if conn, err := Connect(ctx, dialer, opts); err != nil {
-			if err.Error() != "concurrent schema update" {
-				t.Errorf("unexpected error: %s", err)
-			}
-		} else if conn == nil {
-			t.Errorf("conn is nil")
-		} else {
-			conn.Close()
+		switch conn, err := Connect(ctx, dialer, opts); {
+		case err != nil:
+			assert.ErrorIs(t, err, ErrConcurrentSchemaUpdate)
+		case conn == nil:
+			assert.Fail(t, "conn is nil")
+		default:
+			_ = conn.Close()
 		}
 
 		if _, err := fut.Get(); err != nil {