Add swift-testing dependency #153
Description
Sometimes the XCTAssert's output for diff is not very clear.
(For example I have to copy paste a few times from the result of Swift.print or the failure result of XCTAssertEqual to make it happy)
XCTAssertEqual failed: ("Document @1:1-4:2
└─ BlockDirective @1:1-4:2 name: "Image"
├─ Argument text segments:
| @2:1-2:25: " source: "example.png","
| @3:1-3:23: " alt: "Example image""") is not equal to ("Document @1:1-4:2
└─ BlockDirective @1:1-4:2 name: "Image"
├─ Argument text segments:
| @2:1-2:25: " source: \"example.png\","
| @3:1-3:23: " alt: \"Example image\""")I can certainly solve it in the end. But if we can migrate to use swift-testing as our test framework, it will be more clear and more efficient.