build: add __tests__ and __mocks__ dirs to relevant parts of eslint-factory

Signed-off-by: MT Lewis <mtlewis@users.noreply.github.com>

.changeset/great-crews-own.md

@@ -0,0 +1,14 @@
+---
+'@backstage/cli': minor
+---
+
+Treat files in `__tests__` and `__mocks__` directories as test files for linting
+purposes.
+
+Updates the parts of the eslint configuration generator that specify which files
+should be treated as test code to include any files under directories named
+`__tests__` or `__mocks__`, to match the default file locations used in Jest.
+
+cf.
+https://jestjs.io/docs/configuration/#testmatch-arraystring
+https://jestjs.io/docs/manual-mocks#mocking-user-modules

packages/cli/config/eslint-factory.js

@@ -96,12 +96,16 @@ function createConfig(dir, extraConfig = {}) {
                 `!${joinPath(dir, 'src/**')}`,
                 joinPath(dir, 'src/**/*.test.*'),
                 joinPath(dir, 'src/**/*.stories.*'),
+                joinPath(dir, 'src/**/__tests__/**'),
+                joinPath(dir, 'src/**/__mocks__/**'),
                 joinPath(dir, 'src/setupTests.*'),
               ]
             : [
                 // Legacy config for packages that don't provide a dir
                 '**/*.test.*',
                 '**/*.stories.*',
+                '**/__tests__/**',
+                '**/__mocks__/**',
                 '**/src/setupTests.*',
                 '**/dev/**',
               ],
@@ -137,6 +141,8 @@ function createConfig(dir, extraConfig = {}) {
             // Prevent imports of stories or tests
             '*.stories*',
             '*.test*',
+            '**/__tests__/**',
+            '**/__mocks__/**',
           ],
         },
       ],
@@ -159,7 +165,14 @@ function createConfig(dir, extraConfig = {}) {
         },
       },
       {
-        files: ['**/*.test.*', '**/*.stories.*', 'src/setupTests.*', '!src/**'],
+        files: [
+          '**/*.test.*',
+          '**/*.stories.*',
+          '**/__tests__/**',
+          '**/__mocks__/**',
+          'src/setupTests.*',
+          '!src/**',
+        ],
         rules: {
           ...testRules,
           'no-restricted-syntax': [