test: add case to improve coverage

Author: G-Rath

src/rules/utils.ts

@@ -225,12 +225,11 @@ const tryParseAsInvalidConfigError = (
   const [, reason] =
     /ESLint configuration (?:.+) is invalid:(.+)/isu.exec(
       error.message.trim()
-    ) ?? /* istanbul ignore next */ [];
+    ) ?? [];
 
   return reason //
     ? { type: ESLintErrorType.InvalidConfig, reason }
-    : /* istanbul ignore next */
-      null;
+    : null;
 };
 
 const errorParsers: ESLintErrorParser[] = [
@@ -250,10 +249,8 @@ const parseESLintError = (error: Error): ESLintError => {
     }
   }
 
-  /* istanbul ignore next */
   error.message = `Unable to parse error from ESLint: ${error.message}`;
 
-  /* istanbul ignore next */
   throw error;
 };
 

test/helpers.ts

@@ -92,6 +92,23 @@ export const mockEslintPluginPrettier = (): void => {
           create() {
             return {};
           }
+        }),
+        'erroneous-rule': ESLintUtils.RuleCreator(name => name)({
+          name: __filename,
+          meta: {
+            type: 'problem',
+            docs: {
+              description: 'Fake rule that always throws, for use in testing',
+              category: 'Best Practices',
+              recommended: 'warn'
+            },
+            messages: {},
+            schema: []
+          },
+          defaultOptions: [],
+          create() {
+            throw new Error('explosions!');
+          }
         })
       }
     };

test/src/rules/no-invalid-config.spec.ts

@@ -2,10 +2,12 @@ import { TSESLint } from '@typescript-eslint/experimental-utils';
 import dedent from 'dedent';
 import rule from '../../../src/rules/no-invalid-config';
 import { ESLintError, ESLintErrorType } from '../../../src/rules/utils';
-import { RuleTester } from '../../helpers';
+import { RuleTester, mockEslintPluginPrettier } from '../../helpers';
 
 const ruleTester = new RuleTester();
 
+mockEslintPluginPrettier();
+
 const expectedError = ({
   line,
   column,
@@ -20,7 +22,7 @@ const expectedError = ({
   column
 });
 
-ruleTester.run('no-invalid-configs', rule, {
+ruleTester.run('no-invalid-config', rule, {
   valid: [
     'module.exports = undefined;',
     'module.exports = "";',
@@ -75,6 +77,27 @@ ruleTester.run('no-invalid-configs', rule, {
           column: 1
         }
       ]
+    },
+    {
+      code: dedent`
+        module.exports = {
+          plugins: ['prettier'],
+          rules: { 'prettier/erroneous-rule': 'error' }
+        }
+      `,
+      errors: [
+        {
+          messageId: 'UnknownError',
+          data: {
+            message: dedent`
+              Unable to parse error from ESLint: Error while loading rule 'prettier/erroneous-rule': explosions!
+              Occurred while linting <text>
+            `.trim()
+          },
+          line: 1,
+          column: 1
+        }
+      ]
     }
   ]
 });