Failing unit tests with -s flag

[keceli]

Issue Description

This is the same issue originally submitted for Chemist, but now belongs to TensorWrapper.

Various unit tests fail when one runs tests with -s flag although without this flag all these tests pass.

How to Reproduce

> ./test_tensorwrapper -s
.
.
.
/home/keceli/soft/nwx/local/TensorWrapper/tests/sparse_map/sparse_map/sparse_map.cpp:145: PASSED:
  REQUIRE( lhs_v == corr_lhs )
/home/keceli/soft/nwx/local/TensorWrapper/tests/sparse_map/sparse_map/sparse_map.cpp:145: FAILED:
  REQUIRE( lhs_v == corr_lhs )
due to unexpected exception with message:
  PIMPL not set. Did you move from this instance?
.
.
.
/home/keceli/soft/nwx/local/TensorWrapper/tests/sparse_map/sparse_map/sparse_map.cpp:467: PASSED:
  REQUIRE( result == rhs )
/home/keceli/soft/nwx/local/TensorWrapper/tests/sparse_map/sparse_map/sparse_map.cpp:467: FAILED:
  REQUIRE( result == rhs )
due to unexpected exception with message:
  PIMPL not set. Did you move from this instance?

Other Potentially Helpful Information

-s flag is supposed to include successful tests in the output, so these failures might be related to how Catch is handling the output rather than a problem in TensorWrapper.