Add additional test, checking type narrowing

packages/array-partition/index.tests.ts

@@ -7,6 +7,7 @@ const test2: [string[], number[]] = partition(['a', 2, 3, '3'], (x): x is string
 });
 const test3: [number[], number[]] = partition([1, 2, 3, 4], x => typeof x == 'string');
 const test4: [unknown[], unknown[]] = partition([], n => n > 3); // [[], []]
+const test5: [boolean[], number[]] = partition([1, true, 2, 3, true], isBoolean);
 
 // Not OK
 // @ts-expect-error
@@ -21,3 +22,7 @@ partition(null, n => n > 1);
 partition(undefined, n => n > 1);
 // @ts-expect-error
 partition([1, 5, 2, 4, 3], n => n > 3, "a");
+
+function isBoolean(x: unknown): x is boolean {
+  return typeof x === 'boolean';
+}