test: Make analyze tests not depend on GNU date

cloudinit/analyze/dump.py

@@ -50,19 +50,26 @@ def parse_timestamp(timestampstr):
 
     return float(timestamp)
 
+def has_gnu_date():
+    """GNU date includes a string containing the word GNU in it in
+    help output. Posix date does not. Use this to indicate on Linux
+    systems without GNU date that the extended parsing is not
+    available.
+    """
+    return "GNU" in subp.subp(["date", "--help"]).stdout
 
 def parse_timestamp_from_date(timestampstr):
-    cmd = "date"
-    if not util.is_Linux():
-        if subp.which("gdate"):
-            cmd = "gdate"
-        else:
-            raise ValueError(
-                f"Unable to parse timestamp without GNU date: [{timestampstr}]"
-            )
-    out, _ = subp.subp([cmd, "+%s.%3N", "-d", timestampstr])
-    timestamp = out.strip()
-    return float(timestamp)
+    if not util.is_Linux() and subp.which("gdate"):
+        date = "gdate"
+    elif has_gnu_date():
+        date = "date"
+    else:
+        raise ValueError(
+            f"Unable to parse timestamp without GNU date: [{timestampstr}]"
+        )
+    return float(
+        subp.subp([date, "+%s.%3N", "-d", timestampstr]).stdout.strip()
+    )
 
 
 def parse_ci_logline(line):

tests/unittests/analyze/test_dump.py

@@ -9,10 +9,10 @@
     dump_events,
     parse_ci_logline,
     parse_timestamp,
+    has_gnu_date,
 )
-from cloudinit.subp import which
-from cloudinit.util import is_Linux, write_file
-from tests.unittests.helpers import mock, skipIf
+from cloudinit.util import write_file
+from tests.unittests.helpers import mock
 
 
 class TestParseTimestamp:
@@ -43,11 +43,6 @@ def test_parse_timestamp_handles_journalctl_format_adding_year(self):
         dt = datetime.strptime(journal_stamp + " " + str(year), journal_fmt)
         assert float(dt.strftime("%s.%f")) == parse_timestamp(journal_stamp)
 
-    @skipIf(not which("date"), "'date' command not available.")
-    @skipIf(
-        not is_Linux() and not which("gdate"),
-        "'GNU date' command not available.",
-    )
     @pytest.mark.allow_subp_for("date", "gdate")
     def test_parse_unexpected_timestamp_format_with_date_command(self):
         """Dump sends unexpected timestamp formats to date for processing."""
@@ -57,7 +52,11 @@ def test_parse_unexpected_timestamp_format_with_date_command(self):
         year = datetime.now().year
         dt = datetime.strptime(new_stamp + " " + str(year), new_fmt)
 
-        assert float(dt.strftime("%s.%f")) == parse_timestamp(new_stamp)
+        if has_gnu_date():
+            assert float(dt.strftime("%s.%f")) == parse_timestamp(new_stamp)
+        else:
+            with pytest.raises(ValueError):
+                parse_timestamp(new_stamp)
 
 
 class TestParseCILogLine: