Add the missing/extra attribute names to the error message for knownvalue.ObjectExact (#455)

* issue #451 fix

* add changelog

Author: austinvalle

.changes/unreleased/ENHANCEMENTS-20250317-182730.yaml

@@ -0,0 +1,5 @@
+kind: ENHANCEMENTS
+body: 'knownvalue: Updated the `ObjectExact` error message to report extra/missing attributes from the actual object.'
+time: 2025-03-17T18:27:30.206493-04:00
+custom:
+    Issue: "451"

knownvalue/object.go

@@ -5,6 +5,8 @@ package knownvalue
 
 import (
 	"fmt"
+	"maps"
+	"slices"
 	"sort"
 )
 
@@ -24,18 +26,14 @@ func (v objectExact) CheckValue(other any) error {
 	}
 
 	if len(otherVal) != len(v.value) {
-		expectedAttributes := "attributes"
-		actualAttributes := "attributes"
-
-		if len(v.value) == 1 {
-			expectedAttributes = "attribute"
-		}
-
-		if len(otherVal) == 1 {
-			actualAttributes = "attribute"
+		deltaMsg := ""
+		if len(otherVal) > len(v.value) {
+			deltaMsg = createDeltaString(otherVal, v.value, "actual value has extra attribute(s): ")
+		} else {
+			deltaMsg = createDeltaString(v.value, otherVal, "actual value is missing attribute(s): ")
 		}
 
-		return fmt.Errorf("expected %d %s for ObjectExact check, got %d %s", len(v.value), expectedAttributes, len(otherVal), actualAttributes)
+		return fmt.Errorf("expected %d attribute(s) for ObjectExact check, got %d attribute(s): %s", len(v.value), len(otherVal), deltaMsg)
 	}
 
 	var keys []string
@@ -92,3 +90,27 @@ func ObjectExact(value map[string]Check) objectExact {
 		value: value,
 	}
 }
+
+// createDeltaString prints the map keys that are present in mapA and not present in mapB
+func createDeltaString[T any, V any](mapA map[string]T, mapB map[string]V, msgPrefix string) string {
+	deltaMsg := ""
+
+	deltaMap := make(map[string]T, len(mapA))
+	maps.Copy(deltaMap, mapA)
+	for key := range mapB {
+		delete(deltaMap, key)
+	}
+
+	deltaKeys := slices.Sorted(maps.Keys(deltaMap))
+
+	for i, k := range deltaKeys {
+		if i == 0 {
+			deltaMsg += msgPrefix
+		} else if i != 0 {
+			deltaMsg += ", "
+		}
+		deltaMsg += fmt.Sprintf("%q", k)
+	}
+
+	return deltaMsg
+}

knownvalue/object_test.go

@@ -53,9 +53,9 @@ func TestObjectValue_CheckValue(t *testing.T) {
 				"three": knownvalue.Float64Exact(7.89),
 			}),
 			other:         map[string]any{},
-			expectedError: fmt.Errorf("expected 3 attributes for ObjectExact check, got 0 attributes"),
+			expectedError: fmt.Errorf("expected 3 attribute(s) for ObjectExact check, got 0 attribute(s): actual value is missing attribute(s): \"one\", \"three\", \"two\""),
 		},
-		"wrong-length": {
+		"missing-one-attribute": {
 			self: knownvalue.ObjectExact(map[string]knownvalue.Check{
 				"one":   knownvalue.Float64Exact(1.23),
 				"two":   knownvalue.Float64Exact(4.56),
@@ -65,7 +65,47 @@ func TestObjectValue_CheckValue(t *testing.T) {
 				"one": json.Number("1.23"),
 				"two": json.Number("4.56"),
 			},
-			expectedError: fmt.Errorf("expected 3 attributes for ObjectExact check, got 2 attributes"),
+			expectedError: fmt.Errorf("expected 3 attribute(s) for ObjectExact check, got 2 attribute(s): actual value is missing attribute(s): \"three\""),
+		},
+		"missing-multiple-attributes": {
+			self: knownvalue.ObjectExact(map[string]knownvalue.Check{
+				"one":   knownvalue.Float64Exact(1.23),
+				"two":   knownvalue.Float64Exact(4.56),
+				"three": knownvalue.Float64Exact(7.89),
+				"four":  knownvalue.Float64Exact(0.12),
+				"five":  knownvalue.Float64Exact(3.45),
+			}),
+			other: map[string]any{
+				"one": json.Number("1.23"),
+				"two": json.Number("4.56"),
+			},
+			expectedError: fmt.Errorf("expected 5 attribute(s) for ObjectExact check, got 2 attribute(s): actual value is missing attribute(s): \"five\", \"four\", \"three\""),
+		},
+		"extra-one-attribute": {
+			self: knownvalue.ObjectExact(map[string]knownvalue.Check{
+				"one": knownvalue.Float64Exact(1.23),
+				"two": knownvalue.Float64Exact(4.56),
+			}),
+			other: map[string]any{
+				"one":   json.Number("1.23"),
+				"two":   json.Number("4.56"),
+				"three": json.Number("7.89"),
+			},
+			expectedError: fmt.Errorf("expected 2 attribute(s) for ObjectExact check, got 3 attribute(s): actual value has extra attribute(s): \"three\""),
+		},
+		"extra-multiple-attributes": {
+			self: knownvalue.ObjectExact(map[string]knownvalue.Check{
+				"one": knownvalue.Float64Exact(1.23),
+				"two": knownvalue.Float64Exact(4.56),
+			}),
+			other: map[string]any{
+				"one":   json.Number("1.23"),
+				"two":   json.Number("4.56"),
+				"three": json.Number("7.89"),
+				"four":  json.Number("0.12"),
+				"five":  json.Number("3.45"),
+			},
+			expectedError: fmt.Errorf("expected 2 attribute(s) for ObjectExact check, got 5 attribute(s): actual value has extra attribute(s): \"five\", \"four\", \"three\""),
 		},
 		"not-equal": {
 			self: knownvalue.ObjectExact(map[string]knownvalue.Check{