[styles] 100% test coverage

[oliviertassinari]

We don't keep track of the test coverage for the @material-ui/styles package. This has allowed us to quickly ship the new style hook API. It's time to improve the test coverage.

Before
Coverage ~80%

After

After this pull request, I can look into #13607.

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The withStyles() React dev tool overhead is down from 4 components to 2. Thank you React for shipping the hook API!

Before

After

We might get it down to 1 component as we improve the ref story of Material-UI.

[oliviertassinari]

:)

[eps1lon]

Will need to take a closer look at the hook returned from makeStyles.

[eps1lon]

What is the use case for this?

[oliviertassinari]

Commenting the diff would make two tests fail:

24 passing (2s)
  2 failing

  1) withStyles
       integration
         should run lifecycles with no theme:

      AssertionError: expected { root: 'Hook-root-vy1bts' } to deeply equal { root: 'Empty-root-vy1bts' }
      + expected - actual

       {
      -  "root": "Hook-root-vy1bts"
      +  "root": "Empty-root-vy1bts"
       }

      at Context.deepEqual (packages/material-ui-styles/src/withStyles.test.js:80:14)

  2) withStyles
       classname quality
         should use the displayName:

      AssertionError: expected 'Hook' to equal 'a'
      + expected - actual

      -Hook
      +a

      at Context.strictEqual (packages/material-ui-styles/src/withStyles.test.js:219:14)

withStyles uses the display name to provide a meta option.

[eps1lon]

Shouldn't it just override the name then? It seems like the name and meta option are doing the same.

[oliviertassinari]

The name value is human picked. The meta is inferred. The name can have a strong implication on the generated class names in production, the meta is only used for improving the debugging experience.

[eps1lon]

Can we change the name of meta then? It's a pretty generic term. What speaks against using inferredName?

[oliviertassinari]

The meta comes from JSS: https://cssinjs.org/jss-api?v=v10.0.0-alpha.10#create-style-sheet. We can replace it with classNamePrefix in this case?