Fix parsing of dates not parsed by the YAML parser itself

The documentation told users they could use such dates but the
implementation didn't allow that.

src/strava_gear/input/rules.py

@@ -72,7 +72,13 @@
 
 @config_format_checker.checks('datetime')
 def format_checker_datetime(d):
-    return isinstance(d, (datetime.datetime, datetime.date,))
+    if isinstance(d, str):
+        try:
+            return parse_datetime(d) is not None
+        except Exception:
+            return False
+    else:
+        return isinstance(d, (datetime.datetime, datetime.date,))
 
 
 def process_component(k: str, v) -> Component:

tests/test_input_rules.py

@@ -16,6 +16,8 @@ def rd(yaml, **kwargs):
 
 
 def test_minimal():
+    assert rd("rules: [{}]") == Rules(bike_names={}, components=[], rules=[Rule()])
+
     assert rd(
         """
         rules:
@@ -85,7 +87,14 @@ def test_undeclared_components():
     )
 
 
-def test_validation():
+def test_validation_ok():
+    assert rd("rules:\n - since: 2021-01-01")
+    assert rd("rules:\n - since: 2016-05-23T19:30:00+02:00")
+    assert rd("rules:\n - since: 2020-05-01T14:00")
+    assert rd("rules:\n - since: 2020-05-01T14:00+02:00")
+
+
+def test_validation_fails():
     with pytest.raises(ValidationError) as e:
         rd("rules: []")
     assert "[] is too short" in str(e.value)
@@ -100,6 +109,21 @@ def test_validation():
         rd("rules: [{b1: {r1: c1, r2: c1}}]")
     assert "Duplicate components" in str(e.value)
 
+    with pytest.raises(ValidationError) as e:
+        rd("rules: [since:]")
+    assert "is not a 'datetime'" in str(e.value)
+    assert list(e.value.absolute_path) == ['rules', 0, 'since']
+
+    with pytest.raises(ValidationError) as e:
+        rd("rules: [since: 1]")
+    assert "is not a 'datetime'" in str(e.value)
+    assert list(e.value.absolute_path) == ['rules', 0, 'since']
+
+    with pytest.raises(ValidationError) as e:
+        rd("rules: [since: 2021-01-1]")
+    assert "is not a 'datetime'" in str(e.value)
+    assert list(e.value.absolute_path) == ['rules', 0, 'since']
+
     # TODO: more tests for validation