Stop using npm link in tests (#3345)

* Try a custom function

* fix path

* install rsync

* Test with node 8

* Ensure package is removed from the tree

* Remove ours

* matching functions

* try cygwin

* try c:/

* sigh

* Try /cygdrive/

* Try /cygdrive/

* Revert "Try /cygdrive/"

This reverts commit ab1ed779456d39bedbdb128a7aec3bb88b8eeb1c.

* Use sub-optimal copy

* Remove rsync install

* Fix variable

* Continue on err

* Don't link react-scripts, lol

* run yarn after eject

* re-enable cleanup

* uninstall yarn

* try with force

* appveyor ... seriously?

* swallow bad eject

* remove eject error swallow

* Revert "run yarn after eject"

This reverts commit eebf1dbc19aeb6e1f66d5ec27bda2d076bea0956.

* Run yarn after eject

* add a comment

tasks/e2e-kitchensink.sh

@@ -44,6 +44,31 @@ function create_react_app {
   node "$temp_cli_path"/node_modules/create-react-app/index.js "$@"
 }
 
+function install_package {
+  local pkg=$(basename $1)
+
+  # Clean target (for safety)
+  rm -rf node_modules/$pkg/
+  rm -rf node_modules/**/$pkg/
+
+  # Copy package into node_modules/ ignoring installed deps
+  # rsync -a ${1%/} node_modules/ --exclude node_modules
+  cp -R ${1%/} node_modules/
+  rm -rf node_modules/$pkg/node_modules/
+
+  # Install `dependencies`
+  cd node_modules/$pkg/
+  if [ "$USE_YARN" = "yes" ]
+  then
+    yarn install --production
+  else
+    npm install --only=production
+  fi
+  # Remove our packages to ensure side-by-side versions are used (which we link)
+  rm -rf node_modules/{babel-preset-react-app,eslint-config-react-app,react-dev-utils,react-error-overlay,react-scripts}
+  cd ../..
+}
+
 # Check for the existence of one or more files.
 function exists {
   for f in $*; do
@@ -162,13 +187,13 @@ npm install test-integrity@^2.0.1
 cd "$temp_app_path/test-kitchensink"
 
 # Link to our preset
-npm link "$root_path"/packages/babel-preset-react-app
+install_package "$root_path"/packages/babel-preset-react-app
 # Link to error overlay package because now it's a dependency
 # of react-dev-utils and not react-scripts
-npm link "$root_path"/packages/react-error-overlay
+install_package "$root_path"/packages/react-error-overlay
 
 # Link to test module
-npm link "$temp_module_path/node_modules/test-integrity"
+install_package "$temp_module_path/node_modules/test-integrity"
 
 # Test the build
 REACT_APP_SHELL_ENV_MESSAGE=fromtheshell \
@@ -219,23 +244,25 @@ E2E_FILE=./build/index.html \
 # Finally, let's check that everything still works after ejecting.
 # ******************************************************************************
 
-# Unlink our preset
-npm unlink "$root_path"/packages/babel-preset-react-app
-# Unlink error overlay
-npm unlink "$root_path"/packages/react-error-overlay
-
 # Eject...
 echo yes | npm run eject
 
+# Ensure Yarn is ran after eject; at the time of this commit, we don't run Yarn
+# after ejecting. Soon, we may only skip Yarn on Windows. Let's try to remove
+# this in the near future.
+if hash yarnpkg 2>/dev/null
+then
+  yarn install --check-files
+fi
+
 # ...but still link to the local packages
-npm link "$root_path"/packages/babel-preset-react-app
-npm link "$root_path"/packages/eslint-config-react-app
-npm link "$root_path"/packages/react-error-overlay
-npm link "$root_path"/packages/react-dev-utils
-npm link "$root_path"/packages/react-scripts
+install_package "$root_path"/packages/babel-preset-react-app
+install_package "$root_path"/packages/eslint-config-react-app
+install_package "$root_path"/packages/react-error-overlay
+install_package "$root_path"/packages/react-dev-utils
 
 # Link to test module
-npm link "$temp_module_path/node_modules/test-integrity"
+install_package "$temp_module_path/node_modules/test-integrity"
 
 # Test the build
 REACT_APP_SHELL_ENV_MESSAGE=fromtheshell \