I think people do the "separate directory for tests" thing because test runners have, in the past, shipped with a default configuration to target a test directory, rather than match test files by suffix.
Colocation of test files is the hands down winner and encourages the writing of tests. When you're making a change to a code file, you probably won't think to scour the codebase for relevant tests. If you see the test file right next to source file in your editor, you probably will.
Colocation of test files is the hands down winner and encourages the writing of tests. When you're making a change to a code file, you probably won't think to scour the codebase for relevant tests. If you see the test file right next to source file in your editor, you probably will.