Add a test case for updateMetadata when the a descriptor already has the value as an array but then another instance of the descriptor is to be merged

[NelsonPereira1991]

Dendro Version if known (or site URL)

https://github.com/feup-infolab/dendro/tree/machine-plus-human-identifiers

Please describe the expected behaviour

A test case should be added for when the descriptor state is(example for descriptor bdv:coupledResource):

There are already multiple values for the descriptor (so the value is of type array). When a new instance of the coupledResourced is saved it should be added to the array of values.

Build a test for this case.

Please describe the actual behaviour

This bug is already fixed in the branch https://github.com/feup-infolab/dendro/tree/fix_%23278.
However tests for this specific case must be coded

What steps can be taken to reproduce the issue?

Possible ways to fix the problem (programmers)