Convert 2 tests.
Convert 2 tests.

# Conflicts:
#	physics/discrete_trajectory_test.cpp

pleroy/Principia,pleroy/Principia,mockingbirdnest/Principia,mockingbirdnest/Principia,mockingbirdnest/Principia,mockingbirdnest/Principia,pleroy/Principia,pleroy/Principia