Reduce DRY duplication in unit and property tests

Extract shared test helpers for the Memo post and Set Name behavior
slices: fake wallet/profiles, MemoAction tests, page-controller tests,
page build wiring, and shared property-test invariants. Behavior is
preserved; all unit, property, and acceptance tests pass.

By refactorer.

test/unit/page-build-helpers.js

@@ -0,0 +1,26 @@
+'use strict'
+
+const { fakeWallet } = require('../helpers/fake-wallet')
+
+// Build a page controller wired to a working action and a navigation recorder.
+// Both the New Post and Set Name pages extend PageController and take a single
+// action dependency plus a navigate callback, so the wiring is identical; only
+// the page-specific pieces differ. `cfg` supplies:
+//   Page       - the page controller class (NewPostPage or SetNamePage)
+//   Action     - the action class (MemoPost or MemoSetName)
+//   actionKey  - the page's action dependency key ('memoPost' or 'memoSetName')
+//   storeKey   - the action's store dependency key ('feed' or 'profiles')
+//   storeFactory - () => a fresh store
+function buildPage ({ Page, Action, actionKey, storeKey, storeFactory }) {
+  const wallet = fakeWallet()
+  const store = storeFactory()
+  const action = new Action({ wallet, [storeKey]: store })
+  const navigations = []
+  const page = new Page({
+    [actionKey]: action,
+    navigate: (path) => navigations.push(path)
+  })
+  return { wallet, store, action, page, navigations }
+}
+
+module.exports = { buildPage }