tdf#59323 pptx export: test for datetime footer backwards compatibility

Extends the existing pptx export slide footers test to make sure
exported datetime footers will be importable by previous versions
of Impress.

Change-Id: I0026860adb9bebdacc5b2b10fe5d0bf9d7ab419f
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/118028
Tested-by: Jenkins
Reviewed-by: Jan Holesovsky <kendy@collabora.com>
diff --git a/sd/qa/unit/export-tests-ooxml2.cxx b/sd/qa/unit/export-tests-ooxml2.cxx
index b7d6e0c..b7994dc 100644
--- a/sd/qa/unit/export-tests-ooxml2.cxx
+++ b/sd/qa/unit/export-tests-ooxml2.cxx
@@ -1784,6 +1784,10 @@ void SdOOXMLExportTest2::testTdf59323_slideFooters()
    assertXPath(pXmlDocSlide1, "//p:ph [@type='ftr']", "idx", "2");
    assertXPath(pXmlDocSlide1, "//p:ph [@type='sldNum']", "idx", "3");

    // Test if datetime fields have text in them
    // This is needed for backwards compatibility
    assertXPath(pXmlDocSlide1, "//a:fld [@type='datetime1']/a:t");

    xDocShRef->DoClose();
}