feat: add the dsh-superagent research prototype

tests/fixtures/git.ts

@@ -0,0 +1,9 @@
+/** The environment of the git processes the tests start. */
+import { GIT_LOCATION } from '../../src/infra/environment.ts'
+
+/**
+ * The process environment with `extra`, and without the variables that tell git which repository to act on (`GIT_LOCATION`):
+ * the tests run inside `git rebase --exec` inherit GIT_DIR, and a `git init` there would reinitialize the repository under test.
+ */
+export const gitEnv = (extra: Record<string, string> = {}): Record<string, string | undefined> =>
+  ({ ...process.env, ...Object.fromEntries(GIT_LOCATION.map(name => [name, undefined])), ...extra })