add test for custom template

runs on all 'remote' tests, which isn't 100% correct,
but should work for now

binderhub/tests/test_main.py

@@ -83,6 +83,17 @@ async def test_main_page(app):
         assert r.status_code == 200, f"{r.status_code} {url}"
 
 
+@pytest.mark.remote
+async def test_custom_template(app):
+    """Check that our custom template is applied
+
+    Assumes testing/k8s-binder-k8s-hub config is applied
+    """
+    r = await async_requests.get(app.url)
+    assert r.status_code == 200
+    assert "test-template" in r.text
+
+
 @pytest.mark.remote
 async def test_about_handler(app):
     # Check that the about page loads