Increase test coverage

[chapulina]

Desired behavior

Our focus for the 2nd half of 2022 is quality assurance. We'll kick this off with a 1-month sprint to increase the test coverage of the entire stack.

Once a library has reached the desired coverage level, we'll turn on coverage requirements for PRs, so new features can't be added without a satisfactory amount of tests.

Target

• Citadel, Fortress and Garden
• All Gazebo libraries
• C++ non-GUI non-vendored non-deprecated code (explicitly excludes Python / QML)
• 90%

Current status

Package	Citadel	Fortress	Garden
gz-cmake	-	-	-
gz-common
gz-fuel-tools
gz-gui
gz-launch
gz-math		-
gz-msgs
gz-physics
gz-plugin		-
gz-rendering
gz-sensors
gz-sim
gz-tools	-	-	-
gz-transport
gz-utils	-
sdformat

Preliminary tasks

• Double-check all codecov badges on each package's README
• Double-check that coverage reports are being generated correctly
  • no missing files
  • no vendored code included
  • correct branches being uploaded to codecov
  • codecov coverage matches local LCOV reports
• Setup coverage requirements at current levels for all libraries

[ahcorde]

Rendering

• [Backport Citadel] Increase TransformControl test converage (#668) gz-rendering#741
• Added shaderType converage gz-rendering#740
• Improved RenderEngine and Mesh coverage gz-rendering#739
• Increased Marker coverage gz-rendering#738
• Improved grid coverage gz-rendering#737
• Improved coverage Arrow and Axis visuals and fixed some warnings gz-rendering#736

Common

• Improved coverage remotery gz-common#467
• Added BVH and STL loader tests gz-common#466
• Increased Image coverage gz-common#465

Sensors

• Improved noise coverage gz-sensors#278
• Improved coverage Lidar gz-sensors#277