[Test] Add integration test: LGraph snapshot (#591)

- Runs basic Litegraph init before performing the snapshot
- Allows a significantly more useful verification of the public API

test/LGraph_constructor.test.ts

@@ -0,0 +1,13 @@
+import { describe } from "vitest"
+import { LGraph } from "@/litegraph"
+import { dirtyTest } from "./testExtensions"
+
+describe("LGraph (constructor only)", () => {
+  dirtyTest("Matches previous snapshot", ({ expect, minimalSerialisableGraph, basicSerialisableGraph }) => {
+    const minLGraph = new LGraph(minimalSerialisableGraph)
+    expect(minLGraph).toMatchSnapshot("minLGraph")
+
+    const basicLGraph = new LGraph(basicSerialisableGraph)
+    expect(basicLGraph).toMatchSnapshot("basicLGraph")
+  })
+})