Adds a test for TimeEntry#spent_on= with invalid string.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@4709 e93f8b46-1217-0410-a6f0-8f06a7374b81

test/unit/time_entry_test.rb

     assert_equal Date.parse("2011-01-14"), c.spent_on
   end
   
+  def test_spent_on_with_invalid_string
+    c = TimeEntry.new
+    c.spent_on = "foo"
+    assert_nil c.spent_on
+  end
+  
   def test_spent_on_with_date
     c = TimeEntry.new
     c.spent_on = Date.today