stream: improve multiple callback error message

When a transform stream's callback is called more than once,
an error is emitted with a somewhat confusing message. This
commit hopes to improve the quality of the error message.

Fixes: https://github.com/nodejs/node/issues/12513
PR-URL: https://github.com/nodejs/node/pull/12520
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/test/parallel/test-stream-transform-callback-twice.js b/test/parallel/test-stream-transform-callback-twice.js
new file mode 100644
index 0000000000..31a4aea29e
--- /dev/null
+++ b/test/parallel/test-stream-transform-callback-twice.js
@@ -0,0 +1,14 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const { Transform } = require('stream');
+const stream = new Transform({
+  transform(chunk, enc, cb) { cb(); cb(); }
+});
+
+stream.on('error', common.mustCall((err) => {
+  assert.strictEqual(err.toString(),
+                     'Error: write callback called multiple times');
+}));
+
+stream.write('foo');