test_nHingedRigidBodyDefaultConfig

Regression test for issue #469: the constructor used to call this->dcm_HB.Identity() as a statement. Eigen::Matrix3d::Identity() is a static factory whose return value was discarded, so the member was left uninitialized instead of defaulting to identity. This test asserts a freshly constructed effector exposes an identity default.

test_nHingedRigidBodyDefaultConfig.test_defaultDcmIsIdentity()

A fresh effector must default dcm_HB to identity.