test: add regression test that ensures the maximum number of steps th…

…e interpreter can process

src/__tests__/vm.test.ts

@@ -1,3 +1,4 @@
+import type { Recurse } from "../util";
 import type { Brainfuck } from "../vm";
 import type { Assert, Equal } from "./assert";
 
@@ -29,3 +30,24 @@ type Output_2 = Brainfuck<Program_2, Input_2>;
 export type Test_Brainfuck_2 = Assert<
   Equal<Output_2, "Hello, world!" | "!dlrow ,olleH" | "Bye" | "eyB">
 >;
+
+type Repeat<S extends string, N extends number> = Recurse<RepeatSub<S, N, "", []>>;
+type RepeatSub<
+  S extends string,
+  N extends number,
+  R extends string,
+  L extends unknown[],
+> = L["length"] extends N ? R : { __rec: RepeatSub<S, N, `${R}${S}`, [...L, unknown]> };
+
+type Reverse<S extends string> = Recurse<ReverseSub<S, "">>;
+// prettier-ignore
+type ReverseSub<S extends string, R extends string> =
+    S extends "" ? R
+  : S extends `${infer A}${infer B}` ? { __rec: ReverseSub<B, `${A}${R}`> }
+  : never;
+
+type Program_3 = ">,[>,]<[.<]";
+type Input_3 = Repeat<"ABCD", 1000>;
+type Output_3 = Brainfuck<Program_3, Input_3>;
+type Expected_3 = Reverse<Input_3>;
+export type Test_Brainfuck_3 = Assert<Equal<Output_3, Expected_3>>;