should validate signed contexts

[ninokeldishvili]

Motivation

Porting legacy tests from ".FlowERC721/signedContext" — test case "should validate multiple signed contexts Porting legacy tests from ".FlowERC721/signedContext" — test case "should validate a signed context"

Solution

Add new tests in foundry

Checks

By submitting this for review, I'm confirming I've done the following:

• [x] made this PR as small as possible
• [x] unit-tested any new functionality
• [x] linked any relevant issues or PRs