add test cases

the test cases cover those mentioned in #27

test/calendars/issue-27-t1.ics

@@ -0,0 +1,42 @@
+BEGIN:VCALENDAR
+METHOD:PUBLISH
+PRODID:Microsoft Exchange Server 2010
+VERSION:2.0
+X-WR-CALNAME:Events
+X-EVOLUTION-DATA-REVISION:2020-04-23T17:43:39.112248Z(2)
+BEGIN:VTIMEZONE
+TZID:W. Europe Standard Time
+BEGIN:STANDARD
+DTSTART:16010101T030000
+TZOFFSETFROM:+0200
+TZOFFSETTO:+0100
+RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
+END:STANDARD
+BEGIN:DAYLIGHT
+DTSTART:16010101T020000
+TZOFFSETFROM:+0100
+TZOFFSETTO:+0200
+RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=3
+END:DAYLIGHT
+END:VTIMEZONE
+
+BEGIN:VEVENT
+UID:3bbe38c205956551730fc9233525fe268296ec02
+DTSTAMP:20200423T174240Z
+DTSTART;TZID=/freeassociation.sourceforge.net/Europe/Berlin:
+ 20200426T140000
+DTEND;TZID=/freeassociation.sourceforge.net/Europe/Berlin:
+ 20200426T143000
+SUMMARY:Reoccur
+SEQUENCE:7
+X-LIC-ERROR;X-LIC-ERRORTYPE=VALUE-PARSE-ERROR:No value for DESCRIPTION 
+ property. Removing entire property:
+CREATED:20200423T174316Z
+LAST-MODIFIED:20200423T174339Z
+X-LIC-ERROR;X-LIC-ERRORTYPE=VALUE-PARSE-ERROR:No value for DESCRIPTION 
+ property. Removing entire property:
+RRULE:FREQ=DAILY;UNTIL=20200429T000000
+EXDATE:20200427T120000Z
+
+END:VEVENT
+END:VCALENDAR

test/calendars/issue-27-t2.ics

@@ -0,0 +1,42 @@
+BEGIN:VCALENDAR
+METHOD:PUBLISH
+PRODID:Microsoft Exchange Server 2010
+VERSION:2.0
+X-WR-CALNAME:Events
+X-EVOLUTION-DATA-REVISION:2020-04-23T17:43:39.112248Z(2)
+BEGIN:VTIMEZONE
+TZID:W. Europe Standard Time
+BEGIN:STANDARD
+DTSTART:16010101T030000
+TZOFFSETFROM:+0200
+TZOFFSETTO:+0100
+RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
+END:STANDARD
+BEGIN:DAYLIGHT
+DTSTART:16010101T020000
+TZOFFSETFROM:+0100
+TZOFFSETTO:+0200
+RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=3
+END:DAYLIGHT
+END:VTIMEZONE
+
+BEGIN:VEVENT
+UID:3bbe38c205956551730fc9233525fe268296ec02
+DTSTAMP:20200423T174240Z
+DTSTART;TZID=/freeassociation.sourceforge.net/Europe/Berlin:
+ 20200426T140000
+DTEND;TZID=/freeassociation.sourceforge.net/Europe/Berlin:
+ 20200426T143000
+SUMMARY:Reoccur
+SEQUENCE:7
+X-LIC-ERROR;X-LIC-ERRORTYPE=VALUE-PARSE-ERROR:No value for DESCRIPTION 
+ property. Removing entire property:
+CREATED:20200423T174316Z
+LAST-MODIFIED:20200423T174339Z
+X-LIC-ERROR;X-LIC-ERRORTYPE=VALUE-PARSE-ERROR:No value for DESCRIPTION 
+ property. Removing entire property:
+RRULE:FREQ=DAILY;UNTIL=20200429T000000Z
+EXDATE:20200427T120000Z
+
+END:VEVENT
+END:VCALENDAR

test/test_issue_27.py

@@ -0,0 +1,31 @@
+"""These tests are for Issue 27
+https://github.com/niccokunzmann/python-recurring-ical-events/issues/27
+
+"""
+
+start_date = (2020, 4, 25)
+end_date =   (2020, 4, 30)
+
+def print_events(events):
+    for event in events:
+        start = event["DTSTART"].dt
+        duration = event["DTEND"].dt - event["DTSTART"].dt
+        print("start {} duration {}".format(start, duration))
+
+
+def test_until_value_with_unknown_timezone_works_with_exdate(calendars):
+    """The until value has no time zone attached."""
+    events = calendars.issue_27_t1.between(start_date, end_date)
+    print_events(events)
+    assert len(events) == 2, "two events, exdate matches one"
+
+
+def test_until_value_with_default_timezone_works_with_exdate(calendars):
+    """The until value uses the default time zone."""
+    events = calendars.issue_27_t2.between(start_date, end_date)
+    print_events(events)
+    assert len(events) == 2, "two events, exdate matches one"
+
+
+
+