private static void readDataFrame(InputStream in) throws Exception {
        final byte[] frameHeader = readBytes(in, 9);
        final int payloadLength = payloadLength(frameHeader);
        final byte[] payloadBuf = readBytes(in, payloadLength);

        assertThat(payloadBuf).containsExactly("foo".getBytes(StandardCharsets.UTF_8));
    }
This test is to check the behavior of the HttpClient when the 'Expect: 100-continue' header is set.
core/src/test/java/com/linecorp/armeria/client/HttpClientExpect100HeaderTest.java