* Add the Truth dependency
* Port Junit test to Truth in the package `com.google.gson` of the module `gson`
* Replace the `assertThat(e.getMessage()).isEqualTo(...)"` with `assertThat(e).hasMessageThat().isEqualTo(...)`
* Minor fixes
Calling InetAddress.getLocalHost() will cause a lookup to occur that may
fail with a java.net.UnknownHostException if the system the test is
running on is not configured correctly.
This is often fixed by echoing "127.0.0.1 $HOSTNAME" to /etc/hosts, but
in this case it seems easier to pick a static IP string to avoid the
lookup entirely and prevent false negatives in the test.
