Implement tests for DEX Module LP command: `collectFees`

[emiliolisk]

Description

collectFees was tested with the following scenarios and expectations as mentioned below:

Scenario	Expectation
Should be successful when all the parameters are correct	Calls token methods and emits feesIncentivesCollected event.
Should fail when positions size is more than MAX_NUM_POSITIONS_FEE_COLLECTION	Exception is thrown.
Should collect fees when executed	Fees are collected and events emitted.

Acceptance Criteria

• Existing and new unit tests are passing

[Naureen1lightcurve]

This issue #278 is already resolved and the last modification is in this commit.