2210 Fix issue w moving elements beyond border

[Adam-Thometz]

See original issue for context

Proposed Changes

Change one line of code in lib/features/rules/BpmnRules.js in the canMove function:

- if (!target)
+ if (target === undefined)

Reasoning

If a user starts dragging an element, the target is undefined. If a user drags an element outside the canvas, the target is null. Since both cases are considered nullish, they will both return true (meaning the user can drop the element). We want the latter case to return false.

Steps to reproduce

1. Wrap elements in a pool
2. Try dragging an element within the pool.
   a. If dragged within, should be successful
   b. If dragged outside the element but within the canvas, should fail
   c. If dragged outside the element AND outside the canvas, should fail

[CLAassistant]

All committers have signed the CLA.

[barmac]

Hi,

Thank you for your PR. Can you please make sure the contribution meets the requirements in CONTRIBUTING?
Specifically, I'd like you to provide a test case to verify the issue is fixed.
The commit message should also adhere to conventional commits guidelines, and end with Closes #issueNumber.

[Adam-Thometz]

Thank you for the feedback @barmac I updated the commit message and added a test to BpmnCreateMoveSnappingSpec.js

[barmac]

Thanks, I will have a look at this again today.

[barmac]

I've reverted the change to the rules, and the test still passes. What we'd like to achieve is that the test is failing without the change you introduced: https://github.com/bpmn-io/bpmn-js/pull/2244/files#diff-6031dc6e8e3d4e38aef3c1dda35e6ff836a6b6be1263157300284d0191a6d5d4R931
Otherwise, the test does not verify the fix as it is passing without any changes to the library code.

[Adam-Thometz]

Would it be possible to view some documentation on how the inject function works? Trying to figure out how to simulate the viewport bc in the test it does move outside but it isn't perceived as a viewport so it doesn't snap back if that makes sense.

[nikku]

@Adam-Thometz inject will execute the test within a previously bootstrapped bpmn-js instance, and allows you to access internal services.

Similar to this:

const bpmnJS = new BpmnModeler();

const testFn = function(eventBus) { ... };

bpmnJS.invoke(testFn);