Add test for bad command groups

src/group_test.ts

@@ -1,7 +1,10 @@
 import { Command } from "./command.ts";
 import { CommandGroup } from "./group.ts";
 import { string } from "./types.ts";
-import { assertEquals } from "https://deno.land/std@0.118.0/testing/asserts.ts";
+import {
+  assertEquals,
+  assertThrows,
+} from "https://deno.land/std@0.118.0/testing/asserts.ts";
 
 const cmd = new Command("Test child.").required(string, "test");
 
@@ -17,6 +20,18 @@ Deno.test("basic command groups", () => {
   assertEquals(secondResult, { second: { test: "test" } });
 });
 
+Deno.test("basic command group errors", () => {
+  const group = new CommandGroup("A test group.")
+    .subcommand("first", cmd)
+    .subcommand("second", cmd);
+
+  assertThrows(() => group.parse(["bad-key", "test"]));
+  assertThrows(() => group.parse(["FIRST", "test"]));
+  assertThrows(() => group.parse(["Second", "test"]));
+  assertThrows(() => group.parse(["first", "test", "too many"]));
+  assertThrows(() => group.parse(["first"]));
+});
+
 Deno.test("command group help output", () => {
   const innerGroup = new CommandGroup("Inner group.")
     .subcommand("first", cmd)