testing/asserts: Add unimplemented and unreachable (#248)

testing/asserts.ts

@@ -283,3 +283,13 @@ export async function assertThrowsAsync(
     throw new Error(msg);
   }
 }
+
+/** Use this to stub out methods that will throw when invoked. */
+export function unimplemented(msg?: string): never {
+  throw new Error(msg || "unimplemented");
+}
+
+/** Use this to assert unreachable code. */
+export function unreachable(): never {
+  throw new Error("unreachable");
+}

testing/asserts_test.ts

@@ -7,7 +7,9 @@ import {
   assertStrContains,
   assertArrayContains,
   assertMatch,
-  assertEquals
+  assertEquals,
+  unimplemented,
+  unreachable
 } from "./asserts.ts";
 import { test } from "./mod.ts";
 // import { assertEquals as prettyAssertEqual } from "./pretty.ts";
@@ -112,3 +114,25 @@ test(function testingAssertStringMatchingThrows() {
   }
   assert(didThrow);
 });
+
+test(function testingAssertsUnimplemented() {
+  let didThrow = false;
+  try {
+    unimplemented();
+  } catch (e) {
+    assert(e.message === "unimplemented");
+    didThrow = true;
+  }
+  assert(didThrow);
+});
+
+test(function testingAssertsUnreachable() {
+  let didThrow = false;
+  try {
+    unreachable();
+  } catch (e) {
+    assert(e.message === "unreachable");
+    didThrow = true;
+  }
+  assert(didThrow);
+});