Testrunner fails to find `clojure.core/pcalls` in unit test even though it works locally

I have a solution to bank-account:

```
(ns bank-account)

(defn open-account []
(atom 0))

(defn close-account [account]
(reset! account nil))

(defn get-balance [account]
@account)

(defn update-balance [account amount]
(swap! account + amount))
```
which works fine when doing `lein test` locally but fails with:

```
----- Error --------------------------------------------------------------------
Type: clojure.lang.ExceptionInfo
Message: Could not resolve symbol: pcalls
Phase: analysis
```
when submitting the solution to the site. I had a different and more verbose solution earlier and it seems to have passed.

`pcalls` is used in one of the unit tests which from what I understand are not user-changeable. Also `pcalls` is part of clojure.core which should be automatically require:d unless explicitly excluded in clojure.

Not sure what is going on here.