Avoid warnings like:
[2130/2168] Compiling libraries/AP_Math/tests/test_math.cpp
../../libraries/AP_Math/tests/test_math.cpp: In member function ‘virtual void MathTest_IsZero_Test::TestBody()’:
../../libraries/AP_Math/tests/test_math.cpp:73:196: warning: converting ‘false’ to pointer type for argument 1 of ‘char
testing::internal::IsNullLiteralHelper(testing::internal::Secret*)’ [-Wconversion-null]
../../libraries/AP_Math/tests/test_math.cpp:74:199: warning: converting ‘false’ to pointer type for argument 1 of ‘char
testing::internal::IsNullLiteralHelper(testing::internal::Secret*)’ [-Wconversion-null]
Use EXPECT_TRUE() and EXPECT_FALSE() from gtest instead.