Setting npmExec to custom only works for `npm` command

[nmccready]

Setting npmExec works fine when calling npm whatever inside of sbt. However when calling compile or test the npmExec defaults to the original default.

...
npmExec := "yarn",
npmCompileCommands := "install",

sbt
sbt:projecta> npm install
[info] Running Task  command 'yarn install' in .
yarn install v1.9.2
[1/4] Resolving packages...
success Already up-to-date.
Done in 0.24s.
[success] Total time: 1 s, completed Jul 30, 2018 12:56:42 PM
sbt:projecta>

Run compile ....

sbt:projecta> compile
.......
[info] Running Task npmCompileCommands command 'npm install' in .
.....

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/nem/.npm/_logs/2018-07-30T16_57_17_326Z-debug.log

This should be using yarn for both npm install and compile. This also is failing for sbt test on a similar configuration .

Any help would be appreciated.

[nmccready]

Note that clean works just fine. It is something with how the task is defined. Where (compile in Compile) and (test in Test) have different behavior.