Add tests for translations in translations.R

[ianmcook]

Add tests for translations in translations.R

[ianmcook]

Thanks for putting some thought into this.

To reduce the repetition of the same boilerplate code in every test, we could define some helper functions. For example, we could have a trio of functions test_parse_expression_tidyverse(), test_parse_expression_base(), and test_parse_expression_generic(). The generic one would simply call both of the other two.

[ianmcook]

Regarding whether to (1) test the translation or (2) test the outcome:

I think (1) is safer and more general. It eliminates the possibility that the particular input values used in the test coincidentally worked but will not work in general.

[StevenHibble]

I'm thinking there are two options for "indirect" translations:

1. Test the translation

test_that("ifnull() function translates correctly", {
  SQL <- "ifnull(a, b)"
  R   <- "ifelse(is.na(a), b, a)"
  expect_equal(parse_expression(SQL, tidy = FALSE), str2lang(R))
  expect_equal(parse_expression(SQL, tidy = TRUE),  str2lang(R))
})

2. Test the outcome

test_that("ifnull() function translates correctly", {
  a <- c(1, 2, NA)
  b <- c(7, 8, 9)
  SQL <- "ifnull(a, b)"
  answer <- c(1, 2, 9)

  untidy <- eval(parse_expression(SQL, tidy = FALSE))
  tidy   <- eval(parse_expression(SQL, tidy = TRUE))
  expect_equal(untidy, answer)
  expect_equal(tidy,   answer)
})

I think I prefer the 2nd option, though it is more involved. Thoughts?