tests fail with error about babel version less than 7.0.0

[happybeing]

Immediately after cloning master:

yarn
yarn test

Fails with errors including:

 FAIL  __tests__/actions/webIds_actions.spec.js
  ● Test suite failed to run

    Requires Babel "^7.0.0-0", but was loaded with "6.26.3". If you are sure you have a compatible version of @babel/core, it is likely that something in your build process is loading the wrong version. Inspect the stack trace of this error to look for the first entry that doesn't mention "@babel/core" or "babel-core" to see what is calling Babel.

      at throwVersionError (node_modules/@babel/helper-plugin-utils/lib/index.js:65:11)
      at Object.assertVersion (node_modules/@babel/helper-plugin-utils/lib/index.js:13:11)
      at _default (node_modules/@babel/plugin-proposal-class-properties/lib/index.js:81:7)
      at node_modules/@babel/helper-plugin-utils/lib/index.js:19:12
      at Function.memoisePluginContainer (node_modules/babel-core/lib/transformation/file/options/option-manager.js:113:13)
      at Function.normalisePlugin (node_modules/babel-core/lib/transformation/file/options/option-manager.js:146:32)
      at node_modules/babel-core/lib/transformation/file/options/option-manager.js:184:30
          at Array.map (<anonymous>)
      at Function.normalisePlugins (node_modules/babel-core/lib/transformation/file/options/option-manager.js:158:20)
      at OptionManager.mergeOptions (node_modules/babel-core/lib/transformation/file/options/option-manager.js:234:36)
      at OptionManager.init (node_modules/babel-core/lib/transformation/file/options/option-manager.js:368:12)
      at File.initOptions (node_modules/babel-core/lib/transformation/file/index.js:212:65)
      at new File (node_modules/babel-core/lib/transformation/file/index.js:135:24)
      at Pipeline.transform (node_modules/babel-core/lib/transformation/pipeline.js:46:16)

I'm using node v8.11.3, yarn 1.15.2, on Ubuntu 18.10.