Currently in the mapviewer, we have the following coordinates systems :
LV95 & LV03 : swissCoordinatesSystems which inherits CustomCoordinateSystem, and in which the function is implemented
WGS84 & webmercator which inherits StandardCoordinateSystem
We should not call for the function outside of a specific projection. I would remove this FIXME.

do i understand this right, that this function will never be called ? so then we should remove either the whole if statement or replace this function call directly with a throw Error call

I think this function will never be called in the current implementation of the mapviewer. There might be a day where we have a Coordinate System which would be both custom, and not swiss. I would at least add a comment for this , and maybe @pakb has another idea for further mitigation.

Regarding the throw Error call, that is the basic function implementation, so this is currently the case: if we reach this place, something went very wrong and it will throw an error.

Ok so I removed the FIXME comment, so it is like it was before. But I can add a comment saying that this case should never be called in theory

this can also work if the array is still empty, and we should make sure it works in both case.

so if legacyCoordinates = []
then the result is [ undefined, 10 ]
is this valid ?

I don't know if it is ['undefined', 10], as when I tried it quickly it gave me in the console something of the form : [, 10], but if you do legacyCoordinates[0], it should give you undefined, yes.

I tried it and it fills the index 0 with undefined, how did you get [, 10] ? is this an empty string then or what is at index 0
so should i add a test to see if the result is [undefined, 10] ?

I tried it in a quick js codepen, and it gave me [ <1 empty item>, 10 ] as a result. Maybe it's an implementation of the codepen to show undefined items in such a way (for example if I had put the coordinates at arrray[250]).

I would test that the result is indeed [undefined, 10]

ok i'll test this thanks

if we want to check it's transformed correctly, we should also make tests which checks that the values are transformed correctly. This means :
we need to set the visibility to 'true'
we need to check that if we set the opacity to a valid value (a value between 0 and 1 as a string)
we need to add a timeConfig to the layerConfig and a timestamp to check that it can be added to the layer

but it is also good to check that if we set invalid values, it work as expected and ignores those values.

I think this has to be done in a unit test of the transformLayerIntoUrlString function and does not belong to this test
do you want me to create also a unit test for the transformLayerIntoUrlString function ?

Well, handleLegacyParameter uses transformLayerIntoUrlString anyway, but we should also test the transformLayerIntoUrlString if it's not already tested.

i just saw that transformLayerIntoUrlString is already tested in the layersParamParser.spec.js unit test. So i think there is nothing else to do

This would be
// Currently, there is no CustomCoordinateSystem which is not a SwissCoordinateSystem, so this case should never be reached.