New readings test data added

[dzheng13341]

Description

3 test data from testing.md added to readings.js:

• should have daily points for 15 minute reading intervals and quantity units with +-inf start/end time & kWh as BTU chained with reverse conversion
• should have daily points for 15 minute reading intervals and raw units with +-inf start/end time & C as Widget with intercept & chained
• should have daily points for 15 minute reading intervals and raw units with +-inf start/end time & C as Widget with intercept & chained & reverse conversions

Tests are successful.

Type of change

(Check the ones that apply by placing an "x" instead of the space in the [ ] so it becomes [x])

• Note merging this changes the database configuration.
• This change requires a documentation update

Checklist

(Note what you have done by placing an "x" instead of the space in the [ ] so it becomes [x]. It is hoped you do all of them.)

• I have followed the OED pull request ideas
• I have removed text in ( ) from the issue request

Limitations

File testing.md should be updated if pull request is accepted.
For conversion c8 ['F', 'C', true, 0.555556, -17.77778, 'Fahrenheit → Celsius'], gave rounding errors so it is better to use
['F', 'C', true, 1/1.8, -32/1.8, 'Fahrenheit → Celsius'] for closer values.

[huss]

I updated the code for changes I thought we should use. This was not the result of the work by @dzheng13341 but what I noticed during the review of previous work.

[huss]

Thanks to @dzheng13341 for their first PR to OED. The work was very good and no issues were found. I have updated the testing design document to mark these three tests as complete.