I can't find a Playground or API Explorer to test the Linked In API. I've tried over the last 2 years or so and given up every time. Is there one?
simple answer is NO, there is no API explorer or playground.
BUT there is however a test company-account from linkedin you could use for the manage-company api calls.
Company Name : DevTestCo
Company URL : https://www.linkedin.com/company/devtestco
Company ID : 2414183
this account requires no oauth authentication and therefor api-calls can be easily tested.