LineMessagingClientBuilder { public LineMessagingClient build() { return new LineMessagingClientImpl( buildRetrofitIface(apiEndPoint, LineMessagingService.class), buildBlobClient()); } @PackagePrivate  LineMessagingClientBuilder(); LineMessagingClientBuilder apiEndPoint(URI apiEndPoint); LineMessagingClientBuilder channelToken(String channelToken); LineMessagingClientBuilder okHttpClientBuilder(
            final @NonNull OkHttpClient.Builder okHttpClientBuilder,
            final boolean addAuthenticationHeader); LineMessagingClient build();  }
@Test public void testBuildWithoutChannelToken() { assertThatThrownBy(() -> { new LineMessagingClientBuilder().build(); }).isInstanceOf(NullPointerException.class) .hasMessageContaining("channelTokenSupplier"); }