[RED] Add test for csv file export endpoint

apps/exportables/tests/test_units/test_exportables.py

 import json
+import csv
+import io
 from rest_framework import status
 from rest_framework.test import APITestCase
 
@@ -6,6 +8,8 @@ from apps.cases.models import CaseSubject
 from apps.cases.tests.factories.case_subjects import CaseSubjectFactory
 from apps.cases.tests.factories.cases import InvestigationCaseFactory
 
+from apps.exportables.renderers import INVESTIGATION_CASE_RENDERER_FIELDS
+
 
 class ExportableViewTest(APITestCase):
     @classmethod
@@ -176,3 +180,21 @@ class ExportableViewTest(APITestCase):
         }
 
         self.assertJSONEqual(response.content, data)
+
+    def test_export_investigation_data_to_csv_all(self):
+        url = "/exportables/investigation-cases-csv/"
+        response = self.client.get(url)
+
+        self.assertEqual(response.status_code, status.HTTP_200_OK)
+        self.assertEqual(
+            response.get('Content-Disposition'),
+            'attachment; filename="cases.csv"'
+        )
+
+        response_content = response.content.decode('utf-8')
+        reader = csv.reader(io.StringIO(response_content))
+        body = list(reader)
+        headers = body.pop(0)
+
+        self.assertEqual(headers, INVESTIGATION_CASE_RENDERER_FIELDS)
+        self.assertEqual(len(body), 5)