Refactor test cases for improved readability and consistency

- Updated test functions in various test files to enhance code clarity by formatting long lines and improving indentation.
- Adjusted assertions to use multi-line formatting for better readability.
- Added new test cases for theme settings API to ensure proper functionality.
- Ensured consistent use of line breaks and spacing across test files for uniformity.

tests/unit/test_currencies.py

@@ -14,7 +14,13 @@ def _cleanup_currencies(db_session):
     db_session.commit()
 
 
-def _assert_currency(payload: Dict[str, object], code: str, name: str, symbol: str | None, is_active: bool) -> None:
+def _assert_currency(
+    payload: Dict[str, object],
+    code: str,
+    name: str,
+    symbol: str | None,
+    is_active: bool,
+) -> None:
     assert payload["code"] == code
     assert payload["name"] == name
     assert payload["is_active"] is is_active
@@ -47,13 +53,21 @@ def test_create_currency_success(api_client, db_session):
 def test_create_currency_conflict(api_client, db_session):
     api_client.post(
         "/api/currencies/",
-        json={"code": "CAD", "name": "Canadian Dollar",
-              "symbol": "$", "is_active": True},
+        json={
+            "code": "CAD",
+            "name": "Canadian Dollar",
+            "symbol": "$",
+            "is_active": True,
+        },
     )
     duplicate = api_client.post(
         "/api/currencies/",
-        json={"code": "CAD", "name": "Canadian Dollar",
-              "symbol": "$", "is_active": True},
+        json={
+            "code": "CAD",
+            "name": "Canadian Dollar",
+            "symbol": "$",
+            "is_active": True,
+        },
     )
     assert duplicate.status_code == 409
 
@@ -61,8 +75,12 @@ def test_create_currency_conflict(api_client, db_session):
 def test_update_currency_fields(api_client, db_session):
     api_client.post(
         "/api/currencies/",
-        json={"code": "GBP", "name": "British Pound",
-              "symbol": "£", "is_active": True},
+        json={
+            "code": "GBP",
+            "name": "British Pound",
+            "symbol": "£",
+            "is_active": True,
+        },
     )
 
     response = api_client.put(
@@ -77,8 +95,12 @@ def test_update_currency_fields(api_client, db_session):
 def test_toggle_currency_activation(api_client, db_session):
     api_client.post(
         "/api/currencies/",
-        json={"code": "AUD", "name": "Australian Dollar",
-              "symbol": "A$", "is_active": True},
+        json={
+            "code": "AUD",
+            "name": "Australian Dollar",
+            "symbol": "A$",
+            "is_active": True,
+        },
     )
 
     response = api_client.patch(
@@ -97,5 +119,7 @@ def test_default_currency_cannot_be_deactivated(api_client, db_session):
         json={"is_active": False},
     )
     assert response.status_code == 400
-    assert response.json()[
-        "detail"] == "The default currency cannot be deactivated."
+    assert (
+        response.json()["detail"]
+        == "The default currency cannot be deactivated."
+    )