Fix strictmode

[Chemaclass]

Q	A
OS	macOS / Linux / Windows
Shell	bash 3.2
bashunit version	0.13

Summary

Adding set -euo pipefail is not possible yet due to some unknown misbehaviours(🐛 ?)
I will rather work in a follow up PR the fix for it, enabling us to merge the changes of this PR.

For example, ./bashunit tests/acceptance/mock_test.sh without debugging mode (set -x):

And with the debug mode enabled we can already see something, but still is not clear how to fix it:

Expected behavior

We should add set -euo pipefail to all bashunit tests.