* 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
One of our favorite users (my employer!) is stuck in a sad situation where they need to serialize objects returned from Gson; this is a workable escape hatch.