[AssertCollection]
Collection to store assertions. See AssertCollection.
.var.name
[character(1)]
Name for x. Defaults to a heuristic to determine
the name using deparse and substitute.
Value
Depending on the function prefix:
If the check is successful, the functions return TRUE. If the check
is not successful, assertNull/assert_null
throws an error message, testNull/test_null
returns FALSE,
and checkNull returns a string with the error message.
The function expect_null always returns an
expectation.