Add validation to form for enforcing chronological order of PoP start and end dates

tests/forms/test_task_order.py

@@ -1,5 +1,8 @@
+import datetime
+
 from atst.forms.task_order import CLINForm
 from atst.models import JEDICLINType
+from atst.utils.localization import translate
 
 import tests.factories as factories
 
@@ -9,3 +12,21 @@ def test_clin_form_jedi_clin_type():
     clin = factories.CLINFactory.create(jedi_clin_type=jedi_type)
     clin_form = CLINForm(obj=clin)
     assert clin_form.jedi_clin_type.data == jedi_type.value
+
+
+def test_clin_form_start_date_before_end_date():
+    invalid_start = datetime.date(2020, 12, 12)
+    invalid_end = datetime.date(2020, 1, 1)
+    invalid_clin = factories.CLINFactory.create(
+        start_date=invalid_start, end_date=invalid_end
+    )
+    clin_form = CLINForm(obj=invalid_clin)
+    assert not clin_form.validate()
+    assert translate("forms.task_order.start_date_error") in clin_form.start_date.errors
+    valid_start = datetime.date(2020, 1, 1)
+    valid_end = datetime.date(2020, 12, 12)
+    valid_clin = factories.CLINFactory.create(
+        start_date=valid_start, end_date=valid_end
+    )
+    valid_clin_form = CLINForm(obj=valid_clin)
+    assert valid_clin_form.validate()