Differentially test linear-time regexp support for CMD

Create a unit test that differentially tests the change in CMD escaping
from "normal" regular expression to linear-time-based regular
expressions (in [1]). To do this properly, the `shescape-previous`
version is downgraded to the version prior to this migration.

[1]: 0f38a42

Author: ericcornelissen

package-lock.json

@@ -96,7 +96,7 @@
     "prettier": "3.7.3",
     "publint": "0.3.18",
     "rollup": "4.60.0",
-    "shescape-previous": "npm:shescape@2.1.10",
+    "shescape-previous": "npm:shescape@2.1.8",
     "sinon": "21.0.3"
   },
   "scripts": {
@@ -139,7 +139,7 @@
     "mutation:unit": "stryker run config/stryker/unit.js",
     "mutation:integration": "npm run transpile && stryker run config/stryker/integration.js",
     "test": "npm-run-all test:*",
-    "test:unit": "ava test/unit/**/*.test.js",
+    "test:unit": "ava --timeout 59m test/unit/**/*.test.js",
     "test:integration": "npm run transpile && ava test/integration/**/*.test.js --timeout 2m",
     "test:e2e": "node script/busybox-sh.js && node script/double-link-sh.js && ava test/e2e/**/*.test.js --timeout 1m",
     "test:compat": "npm-run-all test:compat:*",

package.json

@@ -0,0 +1,55 @@
+/**
+ * @overview Contains differential tests for the migration form standard regular
+ * expressions to linear-time regular expressions in CMD.
+ * @license MIT
+ */
+
+import { testProp } from "@fast-check/ava";
+import * as fc from "fast-check";
+
+import * as old from "../../../node_modules/shescape-previous/src/internal/win/cmd.js";
+import * as upd from "../../../src/internal/win/cmd.js";
+
+const numRuns = 10_000_000;
+
+testProp(
+  "escape functionality is unchanged",
+  [fc.string()],
+  (t, arg) => {
+    const updFn = upd.getEscapeFunction();
+    const oldFn = old.getEscapeFunction();
+
+    const got = updFn(arg);
+    const want = oldFn(arg);
+    t.is(got, want);
+  },
+  { numRuns },
+);
+
+testProp(
+  "quote functionality is unchanged",
+  [fc.string()],
+  (t, arg) => {
+    const updFn = upd.getQuoteFunction();
+    const oldFn = old.getQuoteFunction();
+
+    const got = updFn[0](updFn[1](arg));
+    const want = oldFn[0](oldFn[1](arg));
+    t.is(got, want);
+  },
+  { numRuns },
+);
+
+testProp(
+  "flag protection functionality is unchanged",
+  [fc.string()],
+  (t, arg) => {
+    const updFn = upd.getFlagProtectionFunction();
+    const oldFn = old.getFlagProtectionFunction();
+
+    const got = updFn(arg);
+    const want = oldFn(arg);
+    t.is(got, want);
+  },
+  { numRuns },
+);