Use multiple date formats in DateRange validator

atst/domain/date.py

@@ -0,0 +1,12 @@
+import pendulum
+
+
+def parse_date(data):
+    date_formats = ["YYYY-MM-DD", "MM/DD/YYYY"]
+    for _format in date_formats:
+        try:
+            return pendulum.from_format(data, _format).date()
+        except (ValueError, pendulum.parsing.exceptions.ParserError):
+            pass
+
+    raise ValueError("Unable to parse string {}".format(data))