feat: add missing functions and docs for LazyFrame

[etiennebacher]

No description provided.

[etiennebacher]

@eitsupi I start testing those functions and I find it a bit hard to read this kind of tests:

expect_query_equal(
    .input$select("int32"),
    .data,
    pl$DataFrame(int32 = 1:5)
  )

I think it's a good idea to test LazyFrame and DataFrame functions at once instead of manually copying tests, but the function above cannot take multiple datasets when testing joins for example. In tidypolars I have a simple script that copies test files for DataFrame and replace all occurrences of DataFrame by LazyFrame and more: https://github.com/etiennebacher/tidypolars/blob/main/tests/testthat/setup.R

This way, I can just write tests for DataFrame and it automatically generates the same tests for LazyFrame. It's also easier to see if an error only happens for eager/lazy data since tests appear in different files. What do you think about this approach?

[eitsupi]

Sorry I did not notice the mention.

What do you think about this approach?

I think it's a good idea, but it may be difficult given the support for tests for things like head that behave differently in LazyFrame and DataFrame?

I'm also concerned about the possibility of files being updated on CI if run as part of R CMD check like setup.R, but I think that's a minor issue.

the function above cannot take multiple datasets when testing joins for example.

Could this be addressed by updating the function?