TypeError on td.replace('aws-sdk')

[cwienands]

Description

I have a service that uses aws-sdk (2.278.1 right now). I would like to test-double the aws-sdk dependency in this service so that I can write true unit tests.

Issue

The td.replace('aws-sdk') call in the initialization of the test fixture throws the following exception:

 TypeError: Method get TypedArray.prototype.length called on incompatible receiver [object Object]
  at Uint8Array.get length [as length] (<anonymous>)
  at isArrayLike (C:\Home\TestProject\node_modules\lodash\isArrayLike.js:30:42)
  at keys (C:\Home\TestProject\node_modules\lodash\keys.js:34:10)
  at baseAssign (C:\Home\TestProject\node_modules\lodash\_baseAssign.js:14:39)
  at baseClone (C:\Home\TestProject\node_modules\lodash\_baseClone.js:122:32)
  at Object.clone (C:\Home\TestProject\node_modules\lodash\clone.js:33:10)
  at Object.exports.default (C:\Home\TestProject\node_modules\testdouble\lib\imitate\create-imitation.js:20:33)
  at imitate (C:\Home\TestProject\node_modules\testdouble\lib\imitate\index.js:12:44)
  at C:\Home\TestProject\node_modules\testdouble\lib\imitate\index.js:15:16
  at C:\Home\TestProject\node_modules\testdouble\lib\imitate\overwrite-children\index.js:18:85
  at newValue (C:\Home\TestProject\node_modules\testdouble\lib\imitate\overwrite-children\copy-props.js:30:22)
  at C:\Home\TestProject\node_modules\testdouble\lib\imitate\overwrite-children\copy-props.js:9:36
  at C:\Home\TestProject\node_modules\lodash\transform.js:60:12
  at C:\Home\TestProject\node_modules\lodash\_createBaseFor.js:17:11
  at baseForOwn (C:\Home\TestProject\node_modules\lodash\_baseForOwn.js:13:20)
  at Object.transform (C:\Home\TestProject\node_modules\lodash\transform.js:59:39)
  at Object.exports.default (C:\Home\TestProject\node_modules\testdouble\lib\imitate\overwrite-children\copy-props.js:5:54)
  at Object.exports.default (C:\Home\TestProject\node_modules\testdouble\lib\imitate\overwrite-children\index.js:17:29)
  at imitate (C:\Home\TestProject\node_modules\testdouble\lib\imitate\index.js:14:33)
  at C:\Home\TestProject\node_modules\testdouble\lib\imitate\index.js:15:16
  at C:\Home\TestProject\node_modules\testdouble\lib\imitate\overwrite-children\index.js:18:85
  at newValue (C:\Home\TestProject\node_modules\testdouble\lib\imitate\overwrite-children\copy-props.js:30:22)
  at C:\Home\TestProject\node_modules\testdouble\lib\imitate\overwrite-children\copy-props.js:16:24
  at C:\Home\TestProject\node_modules\lodash\transform.js:60:12
  at C:\Home\TestProject\node_modules\lodash\_createBaseFor.js:17:11
  at baseForOwn (C:\Home\TestProject\node_modules\lodash\_baseForOwn.js:13:20)
  at Object.transform (C:\Home\TestProject\node_modules\lodash\transform.js:59:39)
  at Object.exports.default (C:\Home\TestProject\node_modules\testdouble\lib\imitate\overwrite-children\copy-props.js:5:54)
  at Object.exports.default (C:\Home\TestProject\node_modules\testdouble\lib\imitate\overwrite-children\index.js:17:29)
  at imitate (C:\Home\TestProject\node_modules\testdouble\lib\imitate\index.js:14:33)
  at C:\Home\TestProject\node_modules\testdouble\lib\imitate\index.js:15:16
  at C:\Home\TestProject\node_modules\testdouble\lib\imitate\overwrite-children\index.js:18:85
  at newValue (C:\Home\TestProject\node_modules\testdouble\lib\imitate\overwrite-children\copy-props.js:30:22)
  at C:\Home\TestProject\node_modules\testdouble\lib\imitate\overwrite-children\copy-props.js:16:24
  at C:\Home\TestProject\node_modules\lodash\transform.js:60:12
  at C:\Home\TestProject\node_modules\lodash\_createBaseFor.js:17:11
  at baseForOwn (C:\Home\TestProject\node_modules\lodash\_baseForOwn.js:13:20)
  at Object.transform (C:\Home\TestProject\node_modules\lodash\transform.js:59:39)
  at Object.exports.default (C:\Home\TestProject\node_modules\testdouble\lib\imitate\overwrite-children\copy-props.js:5:54)
  at Object.exports.default (C:\Home\TestProject\node_modules\testdouble\lib\imitate\overwrite-children\index.js:17:29)
  at Object.imitate [as default] (C:\Home\TestProject\node_modules\testdouble\lib\imitate\index.js:14:33)
  at replaceModule (C:\Home\TestProject\node_modules\testdouble\lib\replace\module\index.js:16:38)
  at Object.default_1 [as replace] (C:\Home\TestProject\node_modules\testdouble\lib\replace\index.js:10:33)
  at Context.beforeEach (C:\Home\TestProject\test\wm\gateways\sns-gateway.spec.js:19:22)

Environment

• node -v output: 8.11.1
• npm -v (or yarn --version) output: 5.6.0
• npm ls testdouble (or yarn list testdouble) version: testdouble@3.8.1
• npm ls aws-sdk: aws-sdk@2.278.1

Failing Test

Code-fenced Examples

var td = require('testdouble');

// this call fails with the error message described above.
td.replace('aws-sdk');

[searls]

AFAICT, this is a bug in either lodash or the custom array type used by the aws package, and outside the confines of testdouble's responsibilities. I say that because testdouble.js is not designed to fake third party libraries. Even though it often technically can replace a third-party dep, the behavior isn't supported.

For more info on why see Don't mock what you don't own. For more conversations on this, see #378, #379, #383, #316, #270

[cwienands]

Thanks for the "Don't mock..." link, and you are right about this. Coincidentally, this is exactly what I did to continue development. Wrap the aws-sdk dependency in a gateway class and mock that instead.