On 02/01/2017 02:46 PM, Ramiro Barrantes wrote:
Hello,
I have a function that applies to an S4 object which contains a slot called
@analysis:
function calculation(myObject) {
tmp <- myObjects@analysis
result <- ...operations on analysis...
return result
}
I am writing a unit test for this function. So I was hoping to create a mock
object but I can't figure out how to do it:
test_that("test calculation function", {
mockMyObject<- mock(?????) #I am not sure what to put here
r<-calculation(mockMyObject)
expect_true(r,0.83625)
})
How can I create a mock S4 object??
I don't know of a convenient way to create a mock with functionality
like mocks in other languages. But here's a class
.A = setClass("A", contains="integer")
This creates an instance that might be used as a mock
mock = .A() # same as new("A")
but maybe you have an initialize method (initialize methods are very
tricky to get correct, and many people avoid them, using
plain-old-functions to form an API around object creation; the
plain-old-function finishes by calling the constructor .A() or new("A"))
that has side effects that are inappropriate for your test, mimicked
here with stop()
setMethod("initialize", "A", function(.Object, ...) stop("oops"))
our initial attempts are thwarted
> .A()
Error in initialize(value, ...) : oops
but we could reach into our bag of hacks and try
mock = .Call(methods:::C_new_object, getClassDef("A"))
You would still need to populate slots / data used in your test, e.g.,
slot(mock, ".Data") = 1:4
This is robust to any validity method, since the validity method is not
invoked on direct slot assignment
setValidity("A", function(object) {
if (all(object > 0)) TRUE else "oops2"
})
slot(mock, ".Data") = 0:4 # still works
So something like
mockS4object = function(class, ..., where=topenv(parent.frame())) {
obj <- .Call(
methods:::C_new_object,
getClassDef(class, where=where)
)
args = list(...)
for (nm in names(args))
slot(obj, nm) = args[[nm]]
obj
}
mockS4object("A", .Data=1:4)
Mock objects typically have useful testing properties, like returning
the number of times a slot (field) is accessed. Unfortunately, I don't
have anything to offer for that.
Martin
Thanks in advance,
Ramiro
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