If you look at src\harness\fourslash.ts , you will see how tests are written that test the language services (in tests\ls\fourslash\ ). This file uses the mock host, implemented in src\harness\harness.ts , which controls the environment in which the language service runs. These tests handle things like lists of members and terminations, type information, formatting, renaming, finding links, etc.
Ryan cavanaugh
source share