update all validation tests

equal.go

@@ -1,10 +1,14 @@
 package validate
 
+var (
+	ErrNotEqual = NewError("must be equal to %v")
+)
+
 // Equal validates whether an input value is equal to a comparison value.
 func Equal[T comparable](cmp T) func(T) error {
 	return func(value T) error {
 		if value != cmp {
-			return ErrValueNotAllowed
+			return ErrNotEqual.With(cmp)
 		}
 		return nil
 	}