Show live Bitcoin price in page title

tests/test_health.py

@@ -32,6 +32,23 @@ def test_health_is_independent_of_btcdata():
     assert response.json() == {"status": "up"}
 
 
+def test_home_updates_title_from_latest_price():
+    response = TestClient(main.app).get("/")
+
+    assert response.status_code == 200
+    assert "new MutationObserver(updateTitleFromPrice)" in response.text
+    assert "document.title = price + ' | BTC Price'" in response.text
+
+
+def test_price_fragment_exposes_formatted_price_for_title():
+    html = main.price_json_to_html(
+        '{"price": 67432.1, "prev_price": 67400, "recorded_at": ""}'
+    )
+
+    assert 'data-title-price="$67.432,10"' in html
+    assert ">$67.432,10</p>" in html
+
+
 def test_ready_when_btcdata_is_healthy(monkeypatch):
     request = httpx.Request("GET", "http://btcdata.test/api/health")
     upstream = httpx.Response(200, request=request)