test: stream writable ended state

PR-URL: https://github.com/nodejs/node/pull/8778
Ref: https://github.com/nodejs/node/issues/8686
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-stream-writable-ended-state.js

@@ -0,0 +1,21 @@
+'use strict';
+
+const common = require('../common');
+
+const assert = require('assert');
+const stream = require('stream');
+
+const writable = new stream.Writable();
+
+writable._write = (chunk, encoding, cb) => {
+  assert.strictEqual(writable._writableState.ended, false);
+  cb();
+};
+
+assert.strictEqual(writable._writableState.ended, false);
+
+writable.end('testing ended state', common.mustCall(() => {
+  assert.strictEqual(writable._writableState.ended, true);
+}));
+
+assert.strictEqual(writable._writableState.ended, true);