Cannot read property 'some' of undefined

[CatsMiaow]

• Node.js v14
• jest v26.6.3
• ts-jest v26.5.1
• typescript v4.1.5

const transformer = require('@nestjs/graphql/plugin');

module.exports = {
  name: 'nestjs-graphql-transformer',
  version: 1,
  factory: (cs) => transformer.before({}, cs.tsCompiler.program)
};

TypeError: Cannot read property 'some' of undefined

       6 |   name: 'nestjs-graphql-transformer',
       7 |   version: 1,
    >  8 |   factory: (cs) => transformer.before({}, cs.tsCompiler.program)
         |                                              ^
       9 | };
      10 | 

      at ConfigSet.isTestFile (../node_modules/ts-jest/dist/config/config-set.js:436:40)
      at ../node_modules/ts-jest/dist/compiler/language-service.js:116:55
          at Array.filter (<anonymous>)
      at Object.exports.initializeLanguageServiceInstance (../node_modules/ts-jest/dist/compiler/language-service.js:116:10)
      at Object.exports.createCompilerInstance (../node_modules/ts-jest/dist/compiler/instance.js:51:30)
      at ConfigSet.get (../node_modules/ts-jest/dist/config/config-set.js:396:31)
      at ConfigSet.<anonymous> (../node_modules/ts-jest/dist/utils/memoize.js:44:24)
      at Object.factory (jest.e2e.transformer.js:8:46)
      at ../node_modules/ts-jest/dist/config/config-set.js:267:61
          at Array.map (<anonymous>)

The error does not occur in the 26.4.4 version, but in the latest version of 26.5.1 it does.

ts-jest/src/config/config-set.ts

Lines 193 to 195 in f2808bb

	this._setupTsJestCfg(options)
	this._resolveTsCacheDir()
	this._matchablePatterns = [...this._jestCfg.testMatch, ...this._jestCfg.testRegex].filter(

In _setupTsJestCfg(), astTransformers are processed, after which _matchablePatterns is defined.
Perhaps _matchablePatterns should be defined before that.

v26.4.4 is being processed with different logic.

https://github.com/kulshekhar/ts-jest/blob/v26.4.4/src/config/config-set.ts#L540-L557

[ahnpnl]

Moving up LGTM, PR is welcome.

[ahnpnl]

There is a branch 26.5.2, you can check out that branch for making the PR

[ahnpnl]

Closes via #2373