test that function in r does not work

Question

library(Rcpp)
cppFunction("
    int fib(int n) 
    {
        if (n < 2) 
            return(n);
        return( fib(n-1) + fib(n-2) );
    }
")

My task is to write several tests to show whether the case is wrong or not.

However, the wrong messages are as follows.

Error during wrapup: Test failed: 'Test cppFunction'
* Not expected: 3 not equal to equals(2)
Modes of target, current: function, numeric
target, current do not match when deparsed.
* Not expected: 5 not equal to equals(5)
Modes of target, current: function, numeric
target, current do not match when deparsed.
* Not expected: 10 not equal to equals(55)
Modes of target, current: function, numeric
target, current do not match when deparsed.
* Not expected: 8 code did not generate an error.
* Not expected: 6 code did not generate an error.
* Not expected: 9 code did not generate an error.
###test that###
library(testthat)
context("Test cppFunction")

##do not know why??
test_that("Test cppFunction",{
  expect_equal(3,equals(2))
  expect_equal(5,equals(5))
  expect_equal(10,equals(55))
  expect_error(8,equals(20))
  expect_error(6,equals(7))
  expect_error(9,equals(25))
})

I cannot figure out why the test that does not work.

Answer 1

First of all, you never even call you fib function in the tests. You should have something like

test_that("Test cppFunction",{
  expect_equal(fib(3),2)
  expect_equal(fib(5),5)
  expect_equal(fib(10),55)
})

Also usage of expect_error is wrong, since fib function is not supposed to produce errors as it is implemented now. I suspect that you wanted to test for non-equality. But that does not make sense, if function does not produce the wrong result you expect, it does not mean that function is right. I would advice just to write more expect_equal tests. If you still want to do that, just write something like

expect_false(fib(10) == 22)

In the end your test should look something like

test_that("Test cppFunction",{
  expect_equal(fib(3),2)
  expect_equal(fib(5),5)
  expect_equal(fib(10),55)
  expect_false(fib(8) == 20)
  expect_false(fib(6) == 7)
  expect_false(fib(9) == 25)
})