Mock a user submission to an exercise

This function helps you test your grade_this() and grade_this_code() logic by helping you quickly create the environment that these functions expect when used to grade a user submission to an exercise in a learnr tutorial.

mock_this_exercise(
  .user_code,
  .solution_code = NULL,
  ...,
  .label = "mock",
  .engine = "r",
  setup_global = NULL,
  setup_exercise = NULL
)

Arguments

.user_code	A single string or expression in braces representing the user submission to this exercise.
.solution_code	An optional single string or expression in braces representing the solution code to this exercise.
...	Ignored
.label	The label of the mock exercise, defaults to "mock".
.engine	The engine of the mock exercise, must be "r" but is included here for future compatibility.
setup_global	An optional single string or expression in braces representing the global setup chunk code.
setup_exercise	An optional single string or expression in braces representing the code in the exercise's setup chunk(s).

Value

Returns the checking environment that is expected by grade_this() and grade_this_code(). Both of these functions themselves return a function that gets called on the checking environment. In other words, the object returned by this function can be passed to the function returned from either grade_this() or grade_this_code() to test the grading logic used in either.

Examples

# First we'll create a grading function with grade_this(). The user's code 
# should return the value 42, and we have some specific messages if they're
# close but miss this target. Otherwise, we'll fall back to the default fail
# message, which will include code feedback.
this_grader <-
  grade_this({
    pass_if_equal(42, "Great Work!")
    fail_if_equal(41, "You were so close!")
    fail_if_equal(43, "Oops, just missed!")
    fail()
  })

# Our first mock submission is almost right...
this_grader(mock_this_exercise(.user_code = 41, .solution_code = 42))
#> <gradethis_graded: [Incorrect] You were so close!>

# Our second mock submission is a little too high...
this_grader(mock_this_exercise(.user_code = 43, .solution_code = 42))
#> <gradethis_graded: [Incorrect] Oops, just missed!>

# A third submission takes an unusual path, but arrives at the right answer.
# Notice that you can use braces around an expression.
this_grader(
  mock_this_exercise(
    .user_code = {
      x <- 31
      y <- 11
      x + y
    }, 
    .solution_code = 42
  )
)
#> <gradethis_graded: [Correct] Great Work!>

# Our final submission changes the prompt slightly. Suppose we have provided
# an `x` object in our global setup with a value of 31. We also have a `y`
# object that we create for the user in the exercise setup chunk. We then ask
# the student to add `x` and `y`. What happens if the student subtracts 
# instead? That's what this mock submission tests:
this_grader(
  mock_this_exercise(
    .user_code = x - y,
    .solution_code = x + y,
    setup_global = x <- 31,
    setup_exercise = y <- 11
  )
)
#> <gradethis_graded: [Incorrect]
#>   Incorrect. I expected you to call `+` where you called `-`. Please
#>   try again.
#> >