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.

Usage

mock_this_exercise(
  .user_code,
  .solution_code = NULL,
  ...,
  .label = "mock",
  .engine = "r",
  .stage = "check",
  .result = rlang::missing_arg(),
  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. If the engine is not "r", then .result must be provided explicitly since mock_this_exercise() cannot evaluate the .user_code.

.stage

The stage of the exercise evaluation, defaults to "check". learnr stages are "code_check", "check" or "error_check". When gradethis is used outside of learnr, this variable is typically NULL.

.result

The result of the evaluation of the .user_code. If the .engine is "r", the result will be prepared automatically by evaluating the user code.

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 `-`. But
#>   no need to fret, try it again.
#> >