Better tests for extension mechanism

[gustavdelius]

We need better tests of the extension mechanism. In particular we need tests for getDiet() and getEncounter() because @baldrech appears to have found a bug in them. Romain's example should form the basis of those tests. getDiet() has a very trivial test of its handling of extensions at

mizer/tests/testthat/test-summary_methods.R

Line 265 in 0139505

test_that("getDiet works with additional components", {

. Note how the functions needed in the test need to be set up in an environment.

getEncounter() does not have any tests of its handling of extensions. They should be added to the tests of its basic behaviour at

mizer/tests/testthat/test-project_methods.R

Line 59 in 0139505

# getEncounter --------------------------------------------------------------