Duplicate identifier 'test'

function test(){
    return 1;
}

Why do such test cases report duplicate definitions when using tsc conversion, as follows ** node_modules/@types/mocha/index.d.ts:2620:13 - error TS2300: Duplicate identifier 'test'.

2620 declare var test: Mocha.TestFunction; ~~~~

test2.ts:1:10 1 function test(){ ~~~~ 'test' was also declared here.

test2.ts:1:10 - error TS2300: Duplicate identifier 'test'.

1 function test(){ ~~~~

node_modules/@types/mocha/index.d.ts:2620:13 2620 declare var test: Mocha.TestFunction; ~~~~ 'test' was also declared here.

Found 2 errors. **