[IMP] tests: add test guidelines

[hokolomopo]

Description

Task: 0

review checklist

• feature is organized in plugin, or UI components
• support of duplicate sheet (deep copy)
• in model/core: ranges are Range object, and can be adapted (adaptRanges)
• in model/UI: ranges are strings (to show the user)
• undo-able commands (uses this.history.update)
• multiuser-able commands (has inverse commands and transformations where needed)
• new/updated/removed commands are documented
• exportable in excel
• translations (_t("qmsdf %s", abc))
• unit tested
• clean commented code
• track breaking changes
• doc is rebuild (npm run doc)
• status is correct in Odoo

[robodoo]

[LucasLefevre]

A few other things are worth mentioning IMO:

• tests should be minimal
• tests should not be coupled to implementation details

[LucasLefevre]

Suggested change

	Rather than calling `model.dispatch("UPDATE_CELL", {...})` use the helpers functions inside `commands_helpers.ts`. And if there are no helper for the command you need to dispatch, create one ! It's easier to read in the test, and in the future if (when) the command is changed, only this helper will need to be modified.
	Rather than calling `model.dispatch("UPDATE_CELL", {...})` use the helpers functions inside `commands_helpers.ts`. And if there are no helper for the command you need to dispatch, create one ! It's easier to read in the test. It also decouples the test from the implementation: in the future if (when) the command changes, only this helper needs to be modified.

[LucasLefevre]

standard English typography do not have a space there

Suggested change

	We define custom jest matchers in `jest_extend.ts`, use them !
	We define custom jest matchers in `jest_extend.ts`, use them!