diff --git a/path_not_specified_add_test.go b/path_not_specified_add_test.go
index 040be14..44fb876 100644
--- a/path_not_specified_add_test.go
+++ b/path_not_specified_add_test.go
@@ -390,13 +390,79 @@ func TestPathNotSpecifiedAdd(t *testing.T) {
 			},
 			expectedChanged: true,
 		},
+		// MultiValued Attribute
+		{
+			name: "Add operation - Extension MultiValued Attributes - add",
+			op: scim.PatchOperation{
+				Op: "add",
+				Value: map[string]interface{}{
+					"urn:ivixvi:testSchema": map[string]interface{}{
+						"testString": []interface{}{"value"},
+					},
+				},
+			},
+			data: map[string]interface{}{},
+			expected: map[string]interface{}{
+				"urn:ivixvi:testSchema": map[string]interface{}{
+					"testString": []interface{}{"value"},
+				},
+			},
+			expectedChanged: true,
+		},
+		{
+			name: "Add operation - Extension MultiValued Attributes - merge slice",
+			op: scim.PatchOperation{
+				Op: "add",
+				Value: map[string]interface{}{
+					"urn:ivixvi:testSchema": map[string]interface{}{
+						"testString": []interface{}{"newValue"},
+					},
+				},
+			},
+			data: map[string]interface{}{
+				"urn:ivixvi:testSchema": map[string]interface{}{
+					"testString": []interface{}{"oldValue"},
+				},
+			},
+			expected: map[string]interface{}{
+				"urn:ivixvi:testSchema": map[string]interface{}{
+					"testString": []interface{}{"oldValue", "newValue"},
+				},
+			},
+			expectedChanged: true,
+		},
+		{
+			name: "Add operation - Extension MultiValued Attributes - no changed",
+			op: scim.PatchOperation{
+				Op: "add",
+				Value: map[string]interface{}{
+					"urn:ivixvi:testSchema": map[string]interface{}{
+						"testString": []interface{}{"value"},
+					},
+				},
+			},
+			data: map[string]interface{}{
+				"urn:ivixvi:testSchema": map[string]interface{}{
+					"testString": []interface{}{"value"},
+				},
+			},
+			expected: map[string]interface{}{
+				"urn:ivixvi:testSchema": map[string]interface{}{
+					"testString": []interface{}{"value"},
+				},
+			},
+			expectedChanged: false,
+		},
 	}
 
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {
 			t.Log(tc.name)
 			// Create a Patcher instance with a dummy schema
-			patcher := scimpatch.NewPatcher(schema.CoreUserSchema(), []schema.Schema{schema.ExtensionEnterpriseUser()}, nil)
+			patcher := scimpatch.NewPatcher(schema.CoreUserSchema(), []schema.Schema{
+				schema.ExtensionEnterpriseUser(),
+				TestExtensionSchema,
+			}, nil)
 
 			// Apply the PatchOperation
 			result, changed, err := patcher.Apply(tc.op, tc.data)
diff --git a/schema_test.go b/schema_test.go
new file mode 100644
index 0000000..15a8ea3
--- /dev/null
+++ b/schema_test.go
@@ -0,0 +1,18 @@
+package scimpatch_test
+
+import (
+	"github.com/elimity-com/scim/optional"
+	"github.com/elimity-com/scim/schema"
+)
+
+var TestExtensionSchema = schema.Schema{
+	Description: optional.NewString("test"),
+	ID:          "urn:ivixvi:testSchema",
+	Name:        optional.NewString("test"),
+	Attributes: []schema.CoreAttribute{
+		schema.SimpleCoreAttribute(schema.SimpleStringParams(schema.StringParams{
+			Name:        "testString",
+			MultiValued: true,
+		})),
+	},
+}