Fix property tests and improve generators

lib/datetime/datetime.ex

@@ -245,14 +245,22 @@ defimpl Timex.Protocol, for: DateTime do
     shifted_us = us + shift
     shifted_secs = div(shifted_us, 1_000*1_000) + (applied_offset_ms * -1)
     rem_us = rem(shifted_us, 1_000*1_000)
+    new_precision = 
+      case Timex.DateTime.Helpers.precision(rem_us) do
+        np when np < precision ->
+          precision
+
+        np ->
+          np
+      end
 
     # Convert back to original timezone
-    case raw_convert(shifted_secs, {rem_us, precision}, tz, :wall) do
+    case raw_convert(shifted_secs, {rem_us, new_precision}, tz, :wall) do
       {:error, {:could_not_resolve_timezone, _, _, _}} ->
         # This occurs when the shifted date/time doesn't exist because of a leap forward
         # This doesn't mean the shift is invalid, simply that we need to ask for the right wall time
         # Which in these cases means asking for the time + 1h
-        raw_convert(shifted_secs + 3600, {rem_us, precision}, tz, :wall)
+        raw_convert(shifted_secs + 3600, {rem_us, new_precision}, tz, :wall)
       result ->
         result
     end

lib/datetime/helpers.ex

@@ -92,8 +92,8 @@ defmodule Timex.DateTime.Helpers do
     end
   end
 
-  defp precision(0), do: 0
-  defp precision(n) when is_integer(n) do
+  def precision(0), do: 0
+  def precision(n) when is_integer(n) do
     ns = Integer.to_string(n)
     n_width = byte_size(ns)
     trimmed = byte_size(String.trim_trailing(ns, "0"))

test/helpers/property_helpers.ex

@@ -4,11 +4,18 @@ defmodule PropertyHelpers do
   """
 
   def date_time_generator(:struct) do
-    date_time_generator(:tupple)
-    |> StreamData.map(&Timex.to_datetime/1)
+    [
+      date_time_generator(:tuple),
+      microsecond_generator()
+    ]
+    |> StreamData.fixed_list()
+    |> StreamData.map(fn [{{y, m, d}, {h, mm, s}}, {us, p}] ->
+      {:ok, nd} = NaiveDateTime.new(y, m, d, h, mm, s, {us, p})
+      DateTime.from_naive!(nd, "Etc/UTC")
+    end)
   end
 
-  def date_time_generator(:tupple) do
+  def date_time_generator(:tuple) do
     [
       StreamData.integer(2000..2030),
       StreamData.integer(1..12),
@@ -18,6 +25,9 @@ defmodule PropertyHelpers do
       StreamData.integer(0..59)
     ]
     |> StreamData.fixed_list()
+    |> StreamData.filter(fn [year, month, day, _hour, _minute, _second] ->
+      :calendar.valid_date(year, month, day)
+    end)
     |> StreamData.map(fn [year, month, day, hour, minute, second] ->
       {{year, month, day}, {hour, minute, second}}
     end)
@@ -27,4 +37,15 @@ defmodule PropertyHelpers do
     Timex.timezones()
     |> StreamData.member_of()
   end
-end
+
+  def microsecond_generator() do
+    [
+      StreamData.integer(0..999_999),
+      StreamData.integer(1..6)
+    ]
+    |> StreamData.fixed_list()
+    |> StreamData.map(fn [us, precision] ->
+      {us, precision}
+    end)
+  end
+end

test/set_test.exs

@@ -5,16 +5,16 @@ defmodule SetTests do
 
   property "setting all the properties from the target date should become a target date for a DateTime" do
     check all input_date <- PropertyHelpers.date_time_generator(:struct),
-              {{year, month, day}, {hour, minute, second}} = target_date <- PropertyHelpers.date_time_generator(:tupple) do
+              {{year, month, day}, {hour, minute, second}} = target_date <- PropertyHelpers.date_time_generator(:tuple) do
 
       date = Timex.set(input_date, [year: year, month: month, day: day, hour: hour, minute: minute, second: second])
       assert Timex.to_erl(date) == target_date
     end
   end
 
-  property "setting all the properties from the target date should become a target date for a tupple" do
-    check all input_date <- PropertyHelpers.date_time_generator(:tupple),
-              {{year, month, day}, {hour, minute, second}} = target_date <- PropertyHelpers.date_time_generator(:tupple) do
+  property "setting all the properties from the target date should become a target date for a tuple" do
+    check all input_date <- PropertyHelpers.date_time_generator(:tuple),
+              {{year, month, day}, {hour, minute, second}} = target_date <- PropertyHelpers.date_time_generator(:tuple) do
 
       date = Timex.set(input_date, [year: year, month: month, day: day, hour: hour, minute: minute, second: second])
       assert Timex.to_erl(date) == target_date

test/timex_test.exs

@@ -34,9 +34,9 @@ defmodule TimexTests do
 
   test "subtract milliseconds" do
     time = Timex.to_datetime({{2015, 6, 24}, {14, 27, 52}})
-    time = %{time | microsecond: {910_000, 6}}
+    time = %{time | microsecond: {910_000, 2}}
     subtracted = Timex.subtract(time, Duration.from_milliseconds(10))
-    assert subtracted.microsecond === {900_000, 6}
+    assert subtracted.microsecond === {900_000, 2}
   end
 
   test "weekday" do

test/timezone_test.exs

@@ -69,7 +69,7 @@ defmodule TimezoneTests do
   end
 
   property "convert always returns DateTime or AmbiguousDateTime" do
-    check all input_date <- PropertyHelpers.date_time_generator(:tupple),
+    check all input_date <- PropertyHelpers.date_time_generator(:tuple),
               timezone <- PropertyHelpers.timezone_generator() do
       result = Timezone.convert(input_date, timezone)
       assert match?(%DateTime{}, result) || match?(%Timex.AmbiguousDateTime{}, result)