feat(std/wasi): add start method to Context (#8141)

This adds a start method to the Context to make starting a command less
tedious and yield consistent errors.

Manually setting the memory is still valid for more complex scenarios,
just undocumented for the time being.

1 files changed, 44 insertions, 1 deletions

diff --git a/std/wasi/snapshot_preview1_test.ts b/std/wasi/snapshot_preview1_test.ts
index 0ea57e089..44877117c 100644
--- a/std/wasi/snapshot_preview1_test.ts
+++ b/std/wasi/snapshot_preview1_test.ts
@@ -1,5 +1,6 @@
 // Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
-import { assertEquals } from "../testing/asserts.ts";
+import Context from "./snapshot_preview1.ts";
+import { assertEquals, assertThrows } from "../testing/asserts.ts";
 import { copy } from "../fs/mod.ts";
 import * as path from "../path/mod.ts";
 
@@ -137,3 +138,45 @@ for (const pathname of tests) {
     },
   });
 }
+
+Deno.test("context_start", function () {
+  assertThrows(
+    () => {
+      const context = new Context({});
+      context.start({
+        exports: {
+          _start() {},
+        },
+      });
+    },
+    TypeError,
+    "must provide a memory export",
+  );
+
+  assertThrows(
+    () => {
+      const context = new Context({});
+      context.start({
+        exports: {
+          _initialize() {},
+          memory: new WebAssembly.Memory({ initial: 1 }),
+        },
+      });
+    },
+    TypeError,
+    "export _initialize must not be a function",
+  );
+
+  assertThrows(
+    () => {
+      const context = new Context({});
+      context.start({
+        exports: {
+          memory: new WebAssembly.Memory({ initial: 1 }),
+        },
+      });
+    },
+    TypeError,
+    "export _start must be a function",
+  );
+});