Sensors system not unloaded properly between tests

[iche033]

Environment

• OS Version: Ubuntu 18.04
• Source build - from Add thermal sensor system for configuring thermal camera properties #614. At commit f377905

Description

When running the INTEGRATION_thermal_system test, the 3rd test segfaults. But if the test is run by itself it runs fine and passes.

More info: This integration test has 3 test cases in this commit. The first 2 tests only runs for 1 iteration so the visuals may not have been created yet. However, the 3rd test runs for multiple iterations which actually cause the visuals to be created, it segfaults with a backtrace pointing to ogre when it tries to create any visual.

• Expected behavior: Test should not segfault
• Actual behavior: Test segfaults

I suspect that the sensors system is not unloaded properly in between tests. So when the 3rd test is run and visuals are to be created, it's actually making ogre calls that are outside the rendering thread (the rendering thread is likely still the one created by the first test).

Steps to reproduce

1. Checkout commit f377905 (branched off of ign-gazebo4), or update thermal_system.cc with this version: https://github.com/ignitionrobotics/ign-gazebo/blob/f377905ea2007c08b5400d366fd8d255af495d65/test/integration/thermal_system.cc
2. Run thermal_system integration test, e.g. ./bin/INTEGRATION_thermal_system
3. test crashes

Output

Backtrace points to ogre2 calls when creating vertex buffer which typically suggests that it's not making the rendering call in the rendering thread.