MIL-002: Step 1 - User interface

Review record RC-024 (Go, autonomous mode, not independent).

Task: MIL-002#1
Task: MIL-002#2
Task: MIL-002#3
Task: MIL-002#4

tests/unit/test_app.py

@@ -1,11 +1,27 @@
 """Tests of the entry point.
 
 @file test_app.py
-@brief Checks main of flash_card.presentation.app.
+@brief Checks main of flash_card.presentation.app without opening a window.
 """
 
-from flash_card.presentation.app import main
+import pytest
+
+from flash_card.presentation import app
 
 
-def test_main_returns_zero_without_arguments() -> None:
-    assert main([]) == 0
+class _FakeRoot:
+    def __init__(self) -> None:
+        self.mainloop_calls = 0
+
+    def mainloop(self) -> None:
+        self.mainloop_calls += 1
+
+
+def test_main_runs_main_loop_and_returns_zero(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    root = _FakeRoot()
+    monkeypatch.setattr(app, "create_application", lambda: (root, object()))
+
+    assert app.main([]) == 0
+    assert root.mainloop_calls == 1