Trap ValueError exception in $datetime function and add tests

test/test_script.py

@@ -31,6 +31,11 @@
 
 import copy
 import datetime
+import os
+from unittest import (
+    skipIf,
+    skipUnless,
+)
 from unittest.mock import MagicMock
 
 from test.picardtestcase import PicardTestCase
@@ -54,6 +59,9 @@ from picard.script import (
 )
 
 
+IS_WIN = os.name == 'nt'
+
+
 class _TestTimezone(datetime.tzinfo):
     def utcoffset(self, dt):
         # Set to GMT+2
@@ -1176,6 +1184,41 @@ class ScriptParserTest(PicardTestCase):
             # Restore original datetime object
             datetime.datetime = original_datetime
 
+    @skipUnless(IS_WIN, "windows test")
+    def test_cmd_datetime_windows(self):
+        ''' Test failure specific to Windows only. '''
+        # Save origninal datetime object and substitute one returning
+        # a fixed now() value for testing.
+        original_datetime = datetime.datetime
+        datetime.datetime = _DateTime
+
+        try:
+            context = Metadata()
+            # Tests with invalid format
+            self.assertScriptResultEquals(r"$datetime(\%B \%-d\, \%Y)", "", context)
+        except (AssertionError, ValueError, IndexError) as err:
+            raise err
+        finally:
+            # Restore original datetime object
+            datetime.datetime = original_datetime
+
+    @skipIf(IS_WIN, "non-windows test")
+    def test_cmd_datetime_non_windows(self):
+        # Save origninal datetime object and substitute one returning
+        # a fixed now() value for testing.
+        original_datetime = datetime.datetime
+        datetime.datetime = _DateTime
+
+        try:
+            context = Metadata()
+            # Tests with invalid format
+            self.assertScriptResultEquals(r"$datetime(\%Y-\%-m-\%-d)", "2020-1-2", context)
+        except (AssertionError, ValueError, IndexError) as err:
+            raise err
+        finally:
+            # Restore original datetime object
+            datetime.datetime = original_datetime
+
     def test_multivalue_1(self):
         self.parser.context = Metadata({'foo': ':', 'bar': 'x:yz', 'empty': ''})
         expr = self.parser.parse('a:bc; d:ef')