Tests for two other cases

tests/test_cli.py

@@ -1,5 +1,5 @@
 from shlex import split as shlex_split
-from subprocess import Popen
+from subprocess import Popen, run
 from time import sleep
 from unittest import TestCase
 
@@ -26,3 +26,41 @@ def test_simple_case(self):
             # Because of the javascripty-nature of the app, we can
             # only really inspect the status code.
             self.assertEqual(response.status_code, 200)
+
+    def test_errors_if_both_demo_and_connection_string_included(self):
+        command = (
+            "fk-graph"
+            " --demo"
+            " --connection-string=\"sqlite+pysqlite:///:memory:\""
+            " --table=table_a"
+            " --primary-key=1"
+        )
+        completed_process = run(
+            shlex_split(command),
+            capture_output=True,
+            text=True,
+            timeout=5
+        )
+        self.assertEqual(completed_process.returncode, 2)
+        self.assertIn(
+            "Exactly one of --demo and --connection-string should be used.",
+            completed_process.stderr
+        )
+
+    def test_errors_if_neither_demo_or_connection_string_included(self):
+        command = (
+            "fk-graph"
+            " --table=table_a"
+            " --primary-key=1"
+        )
+        completed_process = run(
+            shlex_split(command),
+            capture_output=True,
+            text=True,
+            timeout=5
+        )
+        self.assertEqual(completed_process.returncode, 2)
+        self.assertIn(
+            "Exactly one of --demo and --connection-string should be used.",
+            completed_process.stderr
+        )