Fix typos in Testing page

[khouari1]

Thank you for contributing to the documentation.

Do the changes you have made apply to both Current and Previous versions?
No

Have you checked all new or changed links?
N/A

Is there anything else you would like us to know?
No

For reference:

• We have an internal contributions guide
• We have a style guide

This week's exciting excerpts from the style guide

• We write in UK English, with Oxford English Dictionary (OED) spellings, grammar and vocabulary.

Use the present tense wherever possible. Only use another tense where it is strictly necessary.

• Present tense (preferred whenever possible): The script creates a new folder.
• Future tense (avoid whenever possible): The script will create a new folder.

[wjhendry]

Big thanks for those