setting options(datatable.integer64="character") with "bit64" package installed could make test.data.table() gives error.
remove this option or just remove package "bit64"(which will skip those test) will avoid this error message.

Error in test.data.table() :

7 errors out of 8567 in 00:01:26 elapsed (00:02:14 cpu) on Sat Jul 6 13:44:31 2019.
[endian==little, sizeof(long double)==16, sizeof(pointer)==8, TZ=Australia/Melbourne, locale='en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8', l10n_info()='MBCS=TRUE; UTF-8=TRUE; Latin-1=FALSE', getDTthreads()='omp_get_num_procs()==4; R_DATATABLE_NUM_PROCS_PERCENT=="" (default 50); R_DATATABLE_NUM_THREADS==""; omp_get_thread_limit()==2147483647; omp_get_max_threads()==4; OMP_THREAD_LIMIT==""; OMP_NUM_THREADS==""; data.table is using 2 threads. This is set on startup, and by setDTthreads(). See ?setDTthreads.; RestoreAfterFork==true'].
Search tests/tests.Rraw for test numbers: 898, 899.1, 899.2, 1017.1, 1449, 1500.1, 1500.2.

Minimal reproducible example

install.package("bit64")
options(datatable.integer64="character") 
test.data.table()

Output of sessionInfo()

R version 3.6.0 (2019-04-26)
Platform: x86_64-apple-darwin18.6.0 (64-bit)
Running under: macOS Mojave 10.14.5

Matrix products: default
BLAS:   /System/Library/Frameworks/Accelerate.framework/Versions/A/Frameworks/vecLib.framework/Versions/A/libBLAS.dylib
LAPACK: /usr/local/Cellar/openblas/0.3.6_1/lib/libopenblasp-r0.3.6.dylib

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] nanotime_0.2.4    bit64_0.9-7       bit_1.1-14        R.utils_2.9.0     R.oo_1.22.0      
[6] R.methodsS3_1.7.1 xts_0.11-2        zoo_1.8-6         data.table_1.12.2

loaded via a namespace (and not attached):
[1] compiler_3.6.0  tools_3.6.0     RcppCCTZ_0.2.5  Rcpp_1.0.1      grid_3.6.0      lattice_0.20-38