Add some tests

Author: TomWright

func_first.go

@@ -25,7 +25,7 @@ var FirstFunc = BasicFunction{
 				value := val.Index(0)
 				res = append(res, value)
 			default:
-				return nil, fmt.Errorf("cannot use first selector on non slice/array types")
+				return nil, fmt.Errorf("cannot use first selector on non slice/array types: %w", &ErrIndexNotFound{Index: 0})
 			}
 		}
 

func_first_test.go

@@ -14,6 +14,22 @@ func TestFirstFunc(t *testing.T) {
 		}),
 	)
 
+	t.Run("NotFound", selectTestErr(
+		"first()",
+		[]interface{}{},
+		&ErrIndexNotFound{
+			Index: 0,
+		}),
+	)
+
+	t.Run("NotFoundOnInvalidType", selectTestErr(
+		"x.first()",
+		map[string]interface{}{"x": "y"},
+		&ErrIndexNotFound{
+			Index: 0,
+		}),
+	)
+
 	original := map[string]interface{}{
 		"name": map[string]interface{}{
 			"first": "Tom",

func_index.go

@@ -16,8 +16,14 @@ func (e ErrIndexNotFound) Error() string {
 }
 
 func (e ErrIndexNotFound) Is(other error) bool {
-	_, ok := other.(*ErrIndexNotFound)
-	return ok
+	o, ok := other.(*ErrIndexNotFound)
+	if !ok {
+		return false
+	}
+	if o.Index >= 0 && o.Index != e.Index {
+		return false
+	}
+	return true
 }
 
 var IndexFunc = BasicFunction{
@@ -57,7 +63,7 @@ var IndexFunc = BasicFunction{
 					value := val.Index(index)
 					res = append(res, value)
 				default:
-					return nil, fmt.Errorf("cannot use index selector on non slice/array types")
+					return nil, fmt.Errorf("cannot use index selector on non slice/array types: %w", &ErrIndexNotFound{Index: index})
 				}
 			}
 		}

func_index_test.go

@@ -14,6 +14,22 @@ func TestIndexFunc(t *testing.T) {
 		}),
 	)
 
+	t.Run("NotFound", selectTestErr(
+		"[0]",
+		[]interface{}{},
+		&ErrIndexNotFound{
+			Index: 0,
+		}),
+	)
+
+	t.Run("NotFoundOnInvalidType", selectTestErr(
+		"[0]",
+		map[string]interface{}{},
+		&ErrIndexNotFound{
+			Index: 0,
+		}),
+	)
+
 	original := map[string]interface{}{
 		"name": map[string]interface{}{
 			"first": "Tom",

func_last.go

@@ -26,7 +26,7 @@ var LastFunc = BasicFunction{
 				value := val.Index(index)
 				res = append(res, value)
 			default:
-				return nil, fmt.Errorf("cannot use last selector on non slice/array types")
+				return nil, fmt.Errorf("cannot use last selector on non slice/array types: %w", &ErrIndexNotFound{Index: 0})
 			}
 		}
 

func_last_test.go

@@ -14,6 +14,22 @@ func TestLastFunc(t *testing.T) {
 		}),
 	)
 
+	t.Run("NotFound", selectTestErr(
+		"last()",
+		[]interface{}{},
+		&ErrIndexNotFound{
+			Index: -1,
+		}),
+	)
+
+	t.Run("NotFoundOnInvalidType", selectTestErr(
+		"x.last()",
+		map[string]interface{}{"x": "y"},
+		&ErrIndexNotFound{
+			Index: 0,
+		}),
+	)
+
 	original := map[string]interface{}{
 		"name": map[string]interface{}{
 			"first": "Tom",

func_property.go

@@ -15,8 +15,14 @@ func (e ErrPropertyNotFound) Error() string {
 }
 
 func (e ErrPropertyNotFound) Is(other error) bool {
-	_, ok := other.(*ErrPropertyNotFound)
-	return ok
+	o, ok := other.(*ErrPropertyNotFound)
+	if !ok {
+		return false
+	}
+	if o.Property != "" && o.Property != e.Property {
+		return false
+	}
+	return true
 }
 
 var PropertyFunc = BasicFunction{
@@ -64,7 +70,7 @@ var PropertyFunc = BasicFunction{
 					}
 					res = append(res, value)
 				default:
-					return nil, fmt.Errorf("cannot use property selector on non map/struct types: %s", val.Kind().String())
+					return nil, fmt.Errorf("cannot use property selector on non map/struct types: %s: %w", val.Kind().String(), &ErrPropertyNotFound{Property: property})
 				}
 			}
 		}

func_property_test.go

@@ -14,6 +14,22 @@ func TestPropertyFunc(t *testing.T) {
 		}),
 	)
 
+	t.Run("NotFound", selectTestErr(
+		"asd",
+		map[string]interface{}{"x": "y"},
+		&ErrPropertyNotFound{
+			Property: "asd",
+		}),
+	)
+
+	t.Run("NotFoundOnString", selectTestErr(
+		"x.asd",
+		map[string]interface{}{"x": "y"},
+		&ErrPropertyNotFound{
+			Property: "asd",
+		}),
+	)
+
 	original := map[string]interface{}{
 		"name": map[string]interface{}{
 			"first": "Tom",