Improve test coverage for matrix exponentiation (#12388)

* #9943 : Adding coverage test for basic_graphs.py

* #9943 : Adding coverage test for basic_graphs.py

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Solve problem of line too long

* Improving coverage for matrix_exponentiation.py

* fix more than one file

* Update matrix_exponentiation.py

* Update matrix_exponentiation.py

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Maxim Smolskiy <mithridatus@mail.ru>