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Re: Testing fontification, indentation, and buffer manipulation

From: Jostein Kjønigsen
Subject: Re: Testing fontification, indentation, and buffer manipulation
Date: Mon, 21 Jan 2019 11:45:39 +0100

Hey Daniele.

In several of the (third-party) major-modes I author or maintain, I use the library "assess" available on MELPA for testing fontification. See: https://melpa.org/#/assess

For testing indentation, I've also created reference-documents and completely reindented them in a test and then  compared the results. This provides some basic (but not complete) coverage, because (depending on the mode) interactive usage may give different results.

An example. Consider the following line of c/java/_javascript_/php/c#-code:

    if (someBool)

The correct indentation for the following line could be:

- the same as the preceeding line if the next line contains an opening bracket ({)
- nested one level deeper if it contains a direct _expression_.

So when pressing enter... Should you indent immediately? And should you then later on correct the indentation if a user creates a block-start marker { ?

I'm not sure what the right answer is, but it is an example of something which will differ in a interactive use-case vs reflowing a completed, existing document.

If your major-mode has cases like this, you will have to write more elaborate tests to ensure these too are handled correctly.

That said: I'm not sure if this is the recommended or canonical approach, but combining these techniques has worked for me in my projects.

Jostein Kjønigsen

address@hidden 🍵 address@hidden

On Sat, Jan 19, 2019, at 4:07 PM, Daniele Nicolodi wrote:
On 15/01/2019 11:45, Yuri Khan wrote:
On Tue, Jan 15, 2019 at 10:52 PM Daniele Nicolodi <address@hidden> wrote:

I am hacking on beancount-mode (a mode to edit Beancount ledger files)
and I would like to write some automated tests to check the
functionality of the minor mode.  I found ERT, but it seems that it does
not offer any facility to easily test fontification, indentation, or
buffer manipulation in general.

Is there any facility that would help in writing such tests?

You might want to look at ledger-mode tests. Its approach to
fontification testing is:

* Create a temporary buffer.
* Put test text into it.
* Harvest it back with fontification properties into a data structure.
* Test that this structure is equal to the golden output.


Thanks Yuri, this is very helpful.


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