Add IsEqual type utility for type tests

Author: aryaemami59

test/typeTestHelpers.ts

@@ -27,6 +27,25 @@ type Equals<T, U> = IsAny<
   never,
   IsAny<U, never, [T] extends [U] ? ([U] extends [T] ? any : never) : never>
 >
+
+export type IsEqual<A, B> = (<G>() => G extends A ? 1 : 2) extends <
+  G
+>() => G extends B ? 1 : 2
+  ? true
+  : false
+
+export type IfEquals<
+  T,
+  U,
+  TypeIfEquals = unknown,
+  TypeIfNotEquals = never
+> = IsEqual<T, U> extends true ? TypeIfEquals : TypeIfNotEquals
+
+export declare const exactType: <T, U>(
+  draft: T & IfEquals<T, U>,
+  expected: U & IfEquals<T, U>
+) => IfEquals<T, U>
+
 export function expectExactType<T>(t: T) {
   return <U extends Equals<T, U>>(u: U) => {}
 }