[spec] clojure.spec.alpha/exercise-fn should emit a bettor error message when no implementation is found for a symbol

Description

Here we get a NullPointerException because although we do have a spec for foo, we don't have an implementation for it, a more descriptive error message would help.

Proposed: Check for a nil function and throw.

Patch: clj-2190.patch

Environment

Clojure 1.9.0-alpha17
test.check 0.10.0-alpha2

Assignee

Unassigned

Reporter

import

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Approval

Vetted

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Code

Affects versions

Priority

Minor
Configure