Fix timestamp test in Python 3.6

Signed-off-by: Alex Nelson <alexander.nelson@nist.gov>

Author: ajnelson-nist

tests/case_file/Makefile

@@ -96,8 +96,11 @@ kb.ttl: \
 	mv _$@ $@
 
 sample.txt.done.log: \
+  $(tests_srcdir)/.venv.done.log \
   sample_txt.py
-	python3 sample_txt.py sample.txt
+	source $(tests_srcdir)/venv/bin/activate \
+	  && python3 sample_txt.py \
+	    sample.txt
 	touch $@
 
 # Display difference between rdflib default output and compacted output.

tests/case_file/sample_txt.py

@@ -17,13 +17,14 @@
 Mtime should be 2010-01-02T03:04:56Z.
 """
 
-import datetime
 import os
 import sys
 
+import dateutil.parser
+
 with open(sys.argv[1], "w") as out_fh:
     out_fh.write("test")
 
-target_datetime = datetime.datetime.fromisoformat("2010-01-02T03:04:56+00:00")
+target_datetime = dateutil.parser.isoparse("2010-01-02T03:04:56+00:00")
 target_timestamp = target_datetime.timestamp()
 os.utime(sys.argv[1], (target_timestamp, target_timestamp))

tests/requirements.txt

@@ -1,2 +1,3 @@
 PyLD
 pytest
+python-dateutil