Fix rounding errors with #travel_to by resetting the usec on any passed time to zero, so we only travel with per-second precision, not anything deeper than that.

Author: David Heinemeier Hansson

activesupport/CHANGELOG.md

@@ -1,3 +1,8 @@
+*   Fix rounding errors with #travel_to by resetting the usec on any passed time to zero, so we only travel
+    with per-second precision, not anything deeper than that.
+    
+    *DHH*
+
 *   Fix ActiveSupport::TestCase not to order users' test cases by default.
     If this change breaks your tests because your tests are order dependent, you need to explicitly call
     ActiveSupport::TestCase.my_tests_are_order_dependent! at the top of your tests.

activesupport/lib/active_support/testing/time_helpers.rb

@@ -78,6 +78,10 @@ def travel(duration, &block)
       # or <tt>Date.today</tt>, in order to honor the application time zone
       # please always use <tt>Time.current</tt> and <tt>Date.current</tt>.)
       #
+      # Note that the usec for the time passed will be set to 0 to prevent rounding
+      # errors with external services, like MySQL (which will round instead of floor,
+      # leading to off-by-one-second errors).
+      #
       # This method also accepts a block, which will return the current time back to its original
       # state at the end of the block:
       #
@@ -90,7 +94,7 @@ def travel_to(date_or_time, &block)
         if date_or_time.is_a?(Date) && !date_or_time.is_a?(DateTime)
           now = date_or_time.midnight.to_time
         else
-          now = date_or_time.to_time
+          now = date_or_time.to_time.change(usec: 0)
         end
 
         simple_stubs.stub_object(Time, :now, now)

activesupport/test/test_test.rb

@@ -188,19 +188,19 @@ def test_time_helper_travel
     expected_time = Time.now + 1.day
     travel 1.day
 
-    assert_equal expected_time, Time.now
+    assert_equal expected_time.to_s(:db), Time.now.to_s(:db)
     assert_equal expected_time.to_date, Date.today
   end
 
   def test_time_helper_travel_with_block
     expected_time = Time.now + 1.day
 
     travel 1.day do
-      assert_equal expected_time, Time.now
+      assert_equal expected_time.to_s(:db), Time.now.to_s(:db)
       assert_equal expected_time.to_date, Date.today
     end
 
-    assert_not_equal expected_time, Time.now
+    assert_not_equal expected_time.to_s(:db), Time.now.to_s(:db)
     assert_not_equal expected_time.to_date, Date.today
   end
 
@@ -235,4 +235,11 @@ def test_time_helper_travel_back
     assert_not_equal expected_time, Time.now
     assert_not_equal Date.new(2004, 11, 24), Date.today
   end
+
+  def test_travel_to_will_reset_the_usec_to_avoid_mysql_rouding
+    travel_to Time.utc(2014, 10, 10, 10, 10, 50, 999999) do
+      assert_equal 50, Time.now.sec
+      assert_equal 0, Time.now.usec
+    end
+  end
 end