test(observability-map): pin the function-declaration walker branch

The fixture asserted the local and the member declaration forms but not the
function declaration, so deleting that branch of the walker left the fixture
test green and failed only the live-tree assertions the fixture exists to
replace. Assert `helper` too, so each branch is pinned by its own name.
Revert-confirmed: removing the branch now fails the fixture test.

Author: 1stvamp

internal-packages/observability-map/fixtures/webappSymbols/app/declares.ts

@@ -1,7 +1,8 @@
 // webappSymbols.test.ts's self-test tree. One name per declaration form, never two forms of the same
 // name: a single `has` assertion cannot say which branch of the walker answered it, so a shared name
-// would let the member branch be deleted with the fixture test still green. `signJWT` is read and
-// declared nowhere, so a walker that collected references as declarations would find it.
+// would let a branch be deleted with the fixture test still green. `helper` covers the function
+// declaration, `createJWT` the local, `mintSessionToken` the member. `signJWT` is read and declared
+// nowhere, so a walker that collected references as declarations would find it.
 export function helper(kind: string): boolean {
   const createJWT = kind === "jwt";
   return createJWT;

internal-packages/observability-map/src/webappSymbols.test.ts

@@ -194,9 +194,10 @@ describe("the names the tool matches on exist in the webapp", () => {
   // even as a local variable, and failed this suite on any pull request that did.
   it("finds a fixture name however it is declared, and rejects one that is only read", () => {
     const names = declaredNames([join(FIXTURES, "app")]);
-    // A name per declaration form. Sharing one across both would pass on either branch alone, and
-    // the member branch is the one with no other cover: several guards are reached through an
-    // object, so deleting it fails only the live-tree assertions this fixture exists to replace.
+    // A name per declaration form, so no branch of the walker is covered only by another's name:
+    // deleting any one of the three fails here rather than in the live-tree assertions this fixture
+    // exists to replace.
+    expect(names.has("helper")).toBe(true);
     expect(names.has("createJWT")).toBe(true);
     expect(names.has("mintSessionToken")).toBe(true);
     expect(names.has("signJWT")).toBe(false);