Lots of packages that are heavily used don't necessarily have their own unit tests, but lots of people use them in their own packages and assume they work. One way to get around this is for the developer to write unit tests for their package that actually test specific required functionality of imported functions.
This is not a type of testing that is usually undertaken, but perhaps should be more widespread in the R ecosystem due to the number of packages that are published as the result of academic papers with little to no unit testing but the methods end up becoming widely accepted.
Lots of packages that are heavily used don't necessarily have their own unit tests, but lots of people use them in their own packages and assume they work. One way to get around this is for the developer to write unit tests for their package that actually test specific required functionality of imported functions.
This is not a type of testing that is usually undertaken, but perhaps should be more widespread in the R ecosystem due to the number of packages that are published as the result of academic papers with little to no unit testing but the methods end up becoming widely accepted.