File ‘RFpredInterval/libs/RFpredInterval.so’:
  Found non-API call to R: ‘STRING_PTR’

Compiled code should not call non-API entry points in R.

See ‘Writing portable packages’ in the ‘Writing R Extensions’ manual,
and section ‘Moving into C API compliance’ for issues with the use of
non-API entry points.
File ‘RFpredInterval/libs/RFpredInterval.so’:
  Found non-API call to R: ‘STRING_PTR’

Compiled code should not call non-API entry points in R.

See ‘Writing portable packages’ in the ‘Writing R Extensions’ manual,
and section ‘Moving into C API compliance’ for issues with the use of
non-API entry points.
File ‘RFpredInterval/libs/RFpredInterval.so’:
  Found non-API call to R: ‘STRING_PTR’

Compiled code should not call non-API entry points in R.

See ‘Writing portable packages’ in the ‘Writing R Extensions’ manual,
and section ‘Moving into C API compliance’ for issues with the use of
non-API entry points.
File ‘RFpredInterval/libs/RFpredInterval.so’:
  Found non-API call to R: ‘STRING_PTR’

Compiled code should not call non-API entry points in R.

See ‘Writing portable packages’ in the ‘Writing R Extensions’ manual,
and section ‘Moving into C API compliance’ for issues with the use of
non-API entry points.
File 'RFpredInterval/libs/x64/RFpredInterval.dll':
  Found non-API call to R: 'STRING_PTR'

Compiled code should not call non-API entry points in R.

See 'Writing portable packages' in the 'Writing R Extensions' manual,
and section 'Moving into C API compliance' for issues with the use of
non-API entry points.
Running 'testthat.R' [11s]
Running the tests in 'tests/testthat.R' failed.
Complete output:
  > library(testthat)
  > library(RFpredInterval)
  RFpredInterval 1.0.8 
  
  > 
  > test_check("RFpredInterval")