I would appreciate a better description. I don't really understand what have you worked on, without checking the code.

be careful with whitespaces :)
there are plenty, I am not going to mark them all

There are still whitespaces in the code

This is not a blocking comment that why it is not marked as an issue, but I believe that the particular symbol is called parentheses.

isn't it missing the closing "bracket" here?
Do you add it differently?

why do you have to set the closing "bracket" via a function and after using it to invalidate it (empty string) ? IMHO this function could be 2 lines

I think you are missing the tests of sql_opne_bracket() and sql_bracket()

Also you can run the following command to find the codestyle issues
phpcs --standard=Lunr src/Lunr

You haven't written unit tests for this function.

Your parentheses open that by the way could be name as start_group() **HINT**
is overwriting your property. You should think more use cases of grouping than the simple one where (a & b)

sql_parentheses_close that could be named sql_group_end() or so **HINT**. It seems that it is doing more than it should. 
Also check line 609 and you'll understand why this won't work with a HAVING condition.

This should be tested in a separate test function. 

where is hardcoded. You could use the appropriate properties.

You are testing only WHERE. What about HAVING and ON?

It's already pretty nice. However, the use case I mentioned "WHERE ((a=1 AND b=2) OR c=3) OR d=4" still is not possible.
Also, beware of those whitespaces.

honestly I think this is overcomplicating things. You already know which property you need to write into, so why not go ahead and just do it rather than delay it?

the point being?

style

if ($is_join)
{
     $this->$condition .= 'ON (';
     $this->is_join = FALSE;
}
else
{
     $this->$condition .= '(';
}

Saves you the trouble of the looping in sql_conditional

style

style

yeah, no

please rebase against http://reviews.lunr.nl/r/152/

that doesn't make any sense. What are you trying to solve here?

please use the conditionalKeywordProvider

Please rebase against master

nitpick, we don't do the strtoupper in sql_conditional so we don't really need it here either. Just assume everything is passed upper case

I don't think this is unit tested.

nitpick, we don't do the strtoupper in sql_conditional so we don't really need it here either. Just assume everything is passed upper case

SQLite3DMLQueryBuilder

ditto

ditto

ditto

ditto

ditto

assertPropertyEquals

assertPropertyEquals (more down in this file)

This test belongs in a different file

What does this test that is not already tested?

wrong file

what does this test that is not already tested?

wrong class in @covers, also a few others in this file

while I appreciate the effort, this is essentially an unrelated change. Please refrain from putting them in the same review in the future. For this time it is fine.

wrong file

wrong file