This method returns the difference between the dates as wxDateSpan, unlike the
existing Subtract() and overloaded operator-() that return wxTimeSpan.
Closes#14704.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72600 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
No real changes, just refactor the code to allow using CPPUNIT_ASSERT_EQUAL
with wxDateTime in other tests in the future.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67989 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775