`assert` is a statement, so no need to wrap it in braces.

But I would personally do it this way:
```python
from cfme.web_ui import toolbar as tb
from utils import error
from i_dont_remember import NoSuchElementException  # selenium

with error.expected(NoSuchElementException):
    toolbar.select("Power")
```
`toolbar.select` returns `True` if it can click, `False` if it can't (dimmed) and raises `NoSuchElementException` when the button is not present.

Also, one line comment should be written like this:
```python
"""Ensures that no power button is displayed on the templates page."""
```