Standardise how words are being emphasised in the describe() or it() blocks of a unit test

[Jozzey]

There has been some inconsistency in how words are being emphasised in the describe() or it() blocks of a unit test.

Following a discussion on our daily dev call we agreed on a standard where the descriptive text would always be wrapped in single quotes. This has been added to our coding convention here https://github.com/DEFRA/water-abstraction-team/blob/main/coding_conventions.md#unit-test-descriptive-text. If there is a word(s) within that text that we want to emphasise then this would be wrapped in double quotes.

This issue deals with fixing this inconsistency in the https://github.com/DEFRA/water-abstraction-system repo.

[Jozzey]