function checkHeader(assert, sHeaderString, sName, sValue) {
		sHeaderString += "\r\n";

		if (sValue) {
			assert.ok(sHeaderString.includes("\r\n" + sName + ": " + sValue + "\r\n"), sName);
		} else {
			assert.notOk(sHeaderString.includes("\r\n" + sName + ": ", sName));
		}
	}
Checks that the header is as expected.

@param {object} assert The QUnit assert object
@param {string} sHeaderString The headers as in XMLHttpRequest#getAllResponseHeaders
@param {string} sName The header name
@param {string} [sValue] The expected header value