How to disable ts-jest process my .js files

Issue :

I place in jest.conf.js such code:

module.exports = {
    ....
    testMatch: ['**/__tests__/**/*.spec.ts'],
    transform: {
        '^.+\\.ts$': 'ts-jest',
    },
    ...
}

Expected behavior :

I want to disable ts-jest process my .js files. It found tests that is .spec.ts, but if test have an import from some package (.js), then ts-jest started to process that import. How can I configure such behavior to disable ts-jest[jest-transformer] for imported modules inside tests? I also tryed to do as warning told me. I tried to add allowJs: false in my tsconfig - but has no effect. How can I fix that on jest.conf.js level?

Debug log:

I always see this in log and tests pass much slower than it was since there was jest/ts-jest23.

ts-jest[jest-transformer] (WARN) Got a `.js` file to compile while `allowJs` option is not set to `true` (file: ....js). To fix this:
  - if you want TypeScript to process JS files, set `allowJs` to `true` in your TypeScript config (usually tsconfig.json)
  - if you do not want TypeScript to process your `.js` files, in your Jest config change the `transform` key which value is `ts-jest` so that it does not match `.js` files anymore

[medinsky]

solved by adding transformIgnorePatterns: ['^.+\\.js$'], in jest.config.js

[trivikr]

Use testMatch instead

The default in Jest 24 is [ "**/__tests__/**/*.[jt]s?(x)", "**/?(*.)+(spec|test).[jt]s?(x)" ] (docs)

To disable JS files, use [ "**/__tests__/**/*.ts?(x)", "**/?(*.)+(spec|test).ts?(x)" ]