Request: an assert_that function that runs in its own environment

[Former user]

This would work similarly to the test_that function in package testthat. With more complicated assertions where there are intermediate steps, I'd like to not pollute the function environment I'm in. It would work something like this:

assertive::assert_that("This complicated assertion holds", {
  tmp <- "a new variable that the rest of the function can't see"
  assertive::is_character(tmp)
})

[Kendon Bell]

Sorry for the anon post - the above is me

[Richard Cotton]

@kendonB

Isn't that what base R's local() function is for?

local({
    tmp <- "a new variable that the rest of the function can't see"
    assertive::is_character(tmp)
})
ls() # no tmp

[Kendon Bell]

Did not know about local. That works.

[Kendon Bell]

The other attractive behavior of the testthat::test_that function is that it allows you to give a custom message for a larger group of assertions. if + is_* + stop() only really works well for a single assertion.

Is this something in assertive that provides this sort of behavior?

[Richard Cotton]

@kendonB Excellent question. You can use assert_engine(). Try something like this

library(assertive)
letters %>%
  assert_engine(predicate = is_character, msg = "x is not a character vector") %>%
  assert_engine(predicate = is_scalar, msg = "x is not of length 1")

[Richard Cotton]

@kendonB If there are several assertions that you often group together, tell me what they are and perhaps they can be added as a single assert_ function.

[Kendon Bell]

Most of situations I run into that involve several assertions that don't already exist are single use. Usually, I'm wanting to test something very specific about a dataset.

[Richard Cotton]

@kendonB If you want more advice on how to make your own custom assertions, it's discussed in Chapter 7 of Testing R Code.