Repository: mui/material-ui (TypeScript) — Bug Fix

Issue:
1.4.1 Texfield multiline jest snapshot tests broken
When upgrading to 1.4.1 all our snapshot tests including a `<TextField multiline />` are broken due to `Error: Uncaught [TypeError: Cannot read property 'scrollHeight' of null]`.
We had similar issues in the past which were related to refs + react-test-renderer, but I couldn't spot any change in 1.4.1 yet which changed the ref logic.

- related #5531
<!-- Checked checkbox should look like this: [x] -->
- [x] This is a v1.x issue. <!-- (v0.x is no longer maintained) -->
- [x] I have searched the [issues](https://github.com/mui-org/material-ui/issues) of this repository and believe that this is not a duplicate.

## Expected Behavior
minor version jump shouldn't break testing setup

## Current Behavior
testing setup is broken

## Steps to Reproduce
Snapshot `<TextField multiline {...props} />` via jest.

## Context
We render snapshots of all our pages to spot changes on component updates.

## Your Environment
| Tech         | Version |
|--------------|---------|
| Material-UI  | v1.4.1  |
| React        |   latest      |



Discussion:
@sakulstra I have removed some defensive checks that looks very much like dead code to me in #12238 and #12239. I doubt the root of the issue is on Material-UI. The component can be mounted just fine on a browser environment.
I am having this issue as well. The issue is caused by the `syncHeightWithShadow` function inside of the `Textarea` component because it is attempting to access it's refs without ensuring that they are actually mounted.

https://github.com/mui-org/material-ui/blob/4eb6628e5be27a6c140c774069ea794d091c48c3/packages/material-ui/src/Input/Textarea.js#L121-L130

Our snapshot tests use Jest/Enzyme to do shallow rendering, which means child components are not mounted so the refs are `null`. There is currently no way for us to fix tests affected by this issue, save for just mocking the `TextArea` component, but that would cause the quality of the test to suffer.

> Our snapshot tests use Jest/Enzyme to do shallow rendering, which means child components are **not mounted** so the refs are null.

@kanzelm3 This error comes from the `componentDidMount()` hook being called. Don't you find that wrong? I have faced the same issue with the Material-UI test suite. I have added: `disableLifecycleMethods: true` for enzyme. IMHO it should be the default value.
Are you OK closing the issue for https://github.com/airbnb/enzyme/issues/1411?
@oliviertassinari I thought about disabling lifecycle methods. The problem I'm facing with that is we depend on the lifecycle methods to perform functional testing on a few of our components. Because we use `storybook` and the `storyshots` addon to perform snapshot testing, if I disable lifecycle methods, I will have to disable them for the entire project. I haven't figured out how to disable them on a per component basis yet, not sure it's possible.
@kanzelm3 With the information I have at hand, I deeply think it's an enzyme issue, but let's make the life easier for everybody. I think that we should be adding the defensive branch logic back 😢 (with a comment this time).

Resolving patch:
diff --git a/.size-limit.js b/.size-limit.js
--- a/.size-limit.js
+++ b/.size-limit.js
@@ -27,7 +27,7 @@ module.exports = [
     name: 'The size of all the modules of material-ui.',
     webpack: true,
     path: 'packages/material-ui/build/index.js',
-    limit: '95.7 KB',
+    limit: '95.8 KB',
   },
   {
     name: 'The main bundle of the docs',
diff --git a/packages/material-ui/src/Input/Textarea.js b/packages/material-ui/src/Input/Textarea.js
--- a/packages/material-ui/src/Input/Textarea.js
+++ b/packages/material-ui/src/Input/Textarea.js
@@ -121,6 +121,13 @@ class Textarea extends React.Component {
   syncHeightWithShadow() {
     const props = this.props;
 
+    // Guarding for **broken** shallow rendering method that call componentDidMount
+    // but doesn't handle refs correctly.
+    // To remove once the shallow rendering has been fixed.
+    if (!this.shadowRef) {
+      return;
+    }
+
     if (this.isControlled) {
       // The component is controlled, we need to update the shallow value.
       this.shadowRef.value = props.value == null ? '' : String(props.value);


Test patch:
diff --git a/packages/material-ui/src/Input/Textarea.test.js b/packages/material-ui/src/Input/Textarea.test.js
--- a/packages/material-ui/src/Input/Textarea.test.js
+++ b/packages/material-ui/src/Input/Textarea.test.js
@@ -28,7 +28,7 @@ describe('<Textarea />', () => {
   let mount;
 
   before(() => {
-    shallow = createShallow({ disableLifecycleMethods: true });
+    shallow = createShallow();
     mount = createMount();
   });