jestjs - Jest custom transformer - can its performance be improved? -

i'm testing performance of custom transformer jest. currently, transformer nothing return code gets jest. transformer has implemented getcachekey function.

here's entire code transformer:

function process(src, path, config, transformoptions) {   return src; } exports.process = process;  function getcachekey(filedata, filepath, configstr, options) {   return crypto.createhash('md5')     .update(filedata + filepath + configstr, 'utf8')     .digest('hex'); } exports.getcachekey = getcachekey; 

link transformer

the jest config, in package.json follows:

"jest": {   "transform": {     "^.+\\.tsx?$": "<rootdir>/ts-transformer.js"   },   "testmatch": [     "<rootdir>/test-jest/**/*.ts"   ],   "modulefileextensions": [     "ts",     "tsx",     "js",     "json"   ] } 

link package.json

when testing setup jest, takes same amount of time , without --no-cache (around 9 seconds)

when testing setup mocha, first run takes around 7 seconds , subsequent runs take around 4 seconds.

in both cases (with jest , mocha), subsequent runs tested without changing source or test file.

my questions:

• shouldn't subsequent jest runs faster due caching?
• is there in transformer preventing improvement in testing duration?
• is there minimum overhead jest incurs clouding issue?

it might faster update pieces (filedata, filepath, configstr) separately there not have copy of file contents on concatenation.

function getcachekey(filedata, filepath, configstr, options) {     const hash = crypto.createhash('md5');     hash.update(filedata);     hash.update(filepath);     hash.update(configstr);     return hash.digest('hex'); } 

note: if encoding not provided, , data string, encoding of 'utf8' enforced.