Fix Time.add/3 for integer unit (#13125)

Author: michallepicki

lib/elixir/lib/calendar/time.ex

@@ -515,8 +515,12 @@ defmodule Time do
 
   def add(%{calendar: calendar, microsecond: {_, precision}} = time, amount_to_add, unit)
       when is_integer(amount_to_add) do
-    if (is_integer(unit) and unit < 1) or
-         unit not in ~w(second millisecond microsecond nanosecond)a do
+    valid? =
+      if is_integer(unit),
+        do: unit > 0,
+        else: unit in ~w(second millisecond microsecond nanosecond)a
+
+    unless valid? do
       raise ArgumentError,
             "unsupported time unit. Expected :hour, :minute, :second, :millisecond, " <>
               ":microsecond, :nanosecond, or a positive integer, got #{inspect(unit)}"

lib/elixir/test/elixir/calendar/time_test.exs

@@ -96,6 +96,8 @@ defmodule TimeTest do
 
     assert Time.add(time, 1, :hour) == ~T[01:00:00.0]
 
+    assert Time.add(time, 1, 10) == ~T[00:00:00.100000]
+
     assert_raise ArgumentError, ~r/Expected :hour, :minute, :second/, fn ->
       Time.add(time, 1, 0)
     end