Asserting Error Conditions

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Description

When testing code, it is not sufficient to check that results are correct, but also that errors or warnings are signalled in appropriate situations. The functions described here provide a convenient facility for doing so. The three functions check that evaluating the supplied expression produces an error, a warning or one of a specified list of conditions, respectively. If the assertion fails, an error is signalled.

Usage

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assertError(expr, verbose = FALSE)
assertWarning(expr, verbose = FALSE)
assertCondition(expr, ..., .exprString = , verbose = FALSE)

Arguments

expr

an unevaluated R expression which will be evaluated via tryCatch(expr, ..).

...

character strings corresponding to the classes of the conditions that would satisfy the assertion; e.g., "error" or "warning". If none are specified, any condition will satisfy the assertion. See the details section.

.exprString

The string to be printed corresponding to expr. By default, the actual expr will be deparsed. Will be omitted if the function is supplied with the actual expression to be tested. If assertCondition() is called from another function, with the actual expression passed as an argument to that function, supply the deparsed version.

verbose

If TRUE, a message is printed when the condition is satisfied.

Details

assertCondition() uses the general condition mechanism to check all the conditions generated in evaluating expr. The occurrence of any of the supplied condition classes among these satisfies the assertion regardless of what other conditions may be signalled.

assertError() is a convenience function for asserting errors; it calls assertCondition().

assertWarning() asserts that a warning will be signalled, but not an error, whereas assertCondition(expr, "warning") will be satisfied even if an error follows the warning. See the examples.

Value

If the assertion is satisfied, a list of all the condition objects signalled is returned, invisibly. See conditionMessage for the interpretation of these objects. Note that all conditions signalled during the evaluation are returned, whether or not they were among the requirements.

Author(s)

John Chambers and Martin Maechler

See Also

stop, warning; signalCondition, tryCatch.

Examples

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  assertError(sqrt("abc"))
  assertWarning(matrix(1:8, 4,3))

  assertCondition( ""-1 ) # ok, any condition would satisfy this

try( assertCondition(sqrt(2), "warning") )
## .. Failed to get warning in evaluating sqrt(2)
     assertCondition(sqrt("abc"), "error")   # ok
try( assertCondition(sqrt("abc"), "warning") )# -> error: had no warning
     assertCondition(sqrt("abc"), "error")
  ## identical to assertError() call above

assertCondition(matrix(1:5, 2,3), "warning")
try( assertCondition(matrix(1:8, 4,3), "error") )
## .. Failed to get expected error ....

## either warning or worse:
assertCondition(matrix(1:8, 4,3), "error","warning") # OK
assertCondition(matrix(1:8, 4, 3), "warning") # OK

## when both are signalled:
ff <- function() { warning("my warning"); stop("my error") }
    assertCondition(ff(), "warning")
## but assertWarning does not allow an error to follow
try(assertWarning(ff()))
    assertCondition(ff(), "error")          # ok
assertCondition(ff(), "error", "warning") # ok (quietly, catching warning)

## assert that assertC..() does not assert [and use *one* argument only]
assertCondition( assertCondition(sqrt( 2   ), "warning") )
assertCondition( assertCondition(sqrt("abc"), "warning"), "error")
assertCondition( assertCondition(matrix(1:8, 4,3), "error"),
                "error")

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