Elixir pry session interrupted because database connection timed out

I was happily following this advice on how to run a pry debugger inside my Phoenix controller tests:

• require IEx in the target file
• add IEx.pry to the desired line
• run the tests inside IEx: iex -S mix test --trace

But after a few seconds this error always appeared:

16:51:08.108 [error] Postgrex.Protocol (#PID<0.250.0>) disconnected: 
** (DBConnection.ConnectionError) owner #PID<0.384.0> timed out because 
it owned the connection for longer than 15000ms

As the message says, the database connection appears to time out at this point and any commands that invoke the database connection will error out with a DBConnection.OwnershipError. How do I tell my database connection not to time out so I can debug my tests in peace?