passif: Collate a test expression with a message and a action.
In dtkaplan/checkr: Facilities for checking R submissions in tutorials

Description Usage Arguments Details Examples

These functions are simply a way to associate a message with a test. The test itself will be evaluated in line_ functions, arg_ functions, check(), etc. For passif(), failif(), and noteif(), the corresponding result will be generated if the test passes. If the test fails, an "ok" result is generated. But for insist(), a passing test will generate an "ok", and a failing test will generate a "fail". The point of insist() is to avoid the need to use double negative with failif(). The double negative is confusing and error prone to many people.

passif(test, message = default_message)

failif(test, message = default_message)

noteif(test, message = default_message)

insist(test, message = "")

`test`	an expression written in terms of values found in the pattern-matching bindings
`message`	a character string containing the message to return.

The message can include components calculated from the bindings. Enclose these in moustaches, e.g. "The {{F}} function is not appropriate for adding." Within a test, the operators == and != in a test have been augmented to deal with language objects such as names. They are translated to be equivalent to "%same_as%". You can refer to the expression being tested with {{expression_string}} and to the test itself as {{test_string}}.

Use insist() to denote necessary but not sufficient conditions Use failif() and passif() for sufficient conditions.

Functions like line_where() produce pronouns (e.g. V, F, Z, E) which can be used in tests. You need to be careful to write your tests in terms of the types of objects that these pronouns are bound to. Some examples:

code <- for_checkr(quote({x <- 2; y <- x^2; z <- x + y}))
my_line <- line_where(code, insist(F == "+", "Where did you use +?"))
check_binding(my_line, `+`(..(x), ..(y)), insist(y == 4, "use 4 for the second argument to +"))
check_binding(my_line, `+`(..(x), ..(y)), insist(y == 5, "use 5 for the second argument to +"))
# or equivalently with a double negative ... fail and y != 4
check_binding(my_line, `+`(..(x), ..(y)), failif(y != 4, "use 4 for the second argument to +"))
line_where( for_checkr(quote(a ~ b)),
      insist(F == "~", "You needed to type a formula with tilde."))
line_where( for_checkr(quote({x <- 1:3; x[2] <- x[3]})),
      insist(Z == "x[2]", "You were supposed to assign to `x[2]`."))