A flag is defined as single logical value.
checkFlag(x, na.ok = FALSE, null.ok = FALSE)check_flag(x, na.ok = FALSE, null.ok = FALSE)
assertFlag(x, na.ok = FALSE, null.ok = FALSE, .var.name = vname(x),
  add = NULL)
assert_flag(x, na.ok = FALSE, null.ok = FALSE, .var.name = vname(x),
  add = NULL)
testFlag(x, na.ok = FALSE, null.ok = FALSE)
test_flag(x, na.ok = FALSE, null.ok = FALSE)
expect_flag(x, na.ok = FALSE, null.ok = FALSE, info = NULL,
  label = vname(x))
[any] Object to check.
[logical(1)]
Are missing values allowed? Default is FALSE.
[logical(1)]
If set to TRUE, x may also be NULL.
In this case only a type check of x is performed, all additional checks are disabled.
[character(1)]
Name of the checked object to print in assertions. Defaults to
the heuristic implemented in vname.
[AssertCollection]
Collection to store assertion messages. See AssertCollection.
[character(1)]
Extra information to be included in the message for the testthat reporter.
See expect_that.
[character(1)]
Name of the checked object to print in messages. Defaults to
the heuristic implemented in vname.
Depending on the function prefix:
 If the check is successful, the functions 
 assertFlag/assert_flag return 
 x invisibly, whereas
 checkFlag/check_flag and 
 testFlag/test_flag return 
 TRUE.
 If the check is not successful, 
 assertFlag/assert_flag
 throws an error message, 
 testFlag/test_flag
 returns FALSE,
 and checkFlag returns a string with the error message.
 The function expect_flag always returns an
 expectation.
This function does not distinguish between
NA, NA_integer_, NA_real_, NA_complex_
NA_character_ and NaN.
Other scalars: checkCount,
  checkInt, checkNumber,
  checkScalarNA, checkScalar,
  checkString