response = client.get("/override1?level1=foo")
    assert response.json() == "foo"
    assert response.headers["content-type"] == "application/x-level-1"
    assert "x-level0" in response.headers
    assert "x-level1" in response.headers
    assert "x-level2" not in response.headers
    assert "x-level3" not in response.headers
    assert "x-level4" not in response.headers
    assert "x-level5" not in response.headers

</p>

<pre>
x.(T)
</pre>

<p>
asserts that <code>x</code> is not <code>nil</code>
and that the value stored in <code>x</code> is of type <code>T</code>.
The notation <code>x.(T)</code> is called a <i>type assertion</i>.
</p>
<p>
More precisely, if <code>T</code> is not an interface type, <code>x.(T)</code> asserts
that the dynamic type of <code>x</code> is <a href="#Type_identity">identical</a>