test correct error

Supplying one prior caused the error to be due to the sum of priors
being greater than 1 (since priors of length 1 are recycled). This tests
if errors are emitted if a mismatch of number of classes and priors exist

tests/testthat/test-validate-priors.R

@@ -37,5 +37,5 @@ test_that("num priors processed correctly", {
   expect_error(process_priors_num(c(0.5, 0.6), factor(c("a", "b"))))
   expect_error(process_priors_num(1, factor(c("a", "b"))))
   expect_no_error(process_priors_num(1.000001, factor("a")))
-  expect_error(process_priors_num(1, factor(c("a", "b"))))
+  expect_error(process_priors_num(c(0.5, 0.5), factor("a")))
 })