@Test
    void contextCaptorAsync() {
        try (ClientRequestContextCaptor ctxCaptor = Clients.newContextCaptor()) {
            asyncStub.emptyCall(EMPTY, StreamRecorder.create());
            final ClientRequestContext ctx = ctxCaptor.get();
            assertThat(ctx.path()).isEqualTo("/armeria.grpc.testing.TestService/EmptyCall");
        }
    }
Must be at least {@link #unaryPayloadLength()}, plus some to account for encoding overhead.
grpc/src/test/java/com/linecorp/armeria/client/grpc/GrpcClientTest.java