test.data.table() fails if datatable.optimize is already set when run

[MichaelChirico]

From here there are tests which depend on options('datatable.optimize') but aren't careful to set/unset this before testing. Undetected since the default of datatable.optimize is set in onLoad.

Simply run:

library(data.table)
options(datatable.optimize = -1)
test.data.table()

There are 4 errors:

Error in test.data.table() :

4 errors out of 8368 in 35.9s elapsed (56.8s cpu) on Sat Feb 16 12:58:59 2019. [endian==little, sizeof(long double)==16, sizeof(pointer)==8, TZ=Asia/Singapore, locale='LC_CTYPE=en_US.UTF-8;LC_NUMERIC=C;LC_TIME=en_US.UTF-8;LC_COLLATE=en_US.UTF-8;LC_MONETARY=en_US.UTF-8;LC_MESSAGES=en_US.UTF-8;LC_PAPER=en_US.UTF-8;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=en_US.UTF-8;LC_IDENTIFICATION=C', l10n_info()='MBCS=TRUE; UTF-8=TRUE; Latin-1=FALSE']. Search tests/tests.Rraw for test numbers: 656, 657, 658, 865.

I'll try and tackle this alongside point 1 of #2572:

Tests involving GForce functions needs to be run with optimisation level 1 and 2, so that both functions are tested all the time.