global: enhance unit test for LazyDict

* Add unit test for the class LazyDict.

Signed-off-by: Leonardo Rossi <leonardo.r@cern.ch>
What if `'.'` or `']'` is in dict?

**Test case**
```python
d = SmartDict({'.': 'dot', ']': 'bracket'})
assert d['.'] == 'dot'
assert d[']'] == 'bracket'
```