From https://once.com/writebook

test/models/book/accessable_test.rb

@@ -0,0 +1,36 @@
+require "test_helper"
+
+class Book::AccessableTest < ActiveSupport::TestCase
+  test "update_access always grants read access to everyone when everyone_access is set" do
+    book = Book.create!(title: "My new book")
+    book.update_access(editors: [], readers: [])
+
+    assert book.everyone_access?
+
+    User.all.each do |user|
+      assert book.accessable?(user: user)
+      assert_not book.editable?(user: user) unless user.administrator?
+    end
+  end
+
+  test "update_access updates existing access" do
+    book = Book.create!(title: "My new book", everyone_access: false)
+
+    book.update_access(editors: [ users(:kevin).id ], readers: [])
+    assert book.editable?(user: users(:kevin))
+
+    book.update_access(editors: [], readers: [ users(:kevin).id ])
+    assert book.accessable?(user: users(:kevin))
+    assert_not book.editable?(user: users(:kevin))
+  end
+
+  test "update_access removes stale accesses" do
+    book = Book.create!(title: "My new book", everyone_access: false)
+
+    book.update_access(editors: [ users(:kevin).id ], readers: [ users(:jz).id ])
+    assert_equal 2, book.accesses.size
+
+    book.update_access(editors: [ users(:kevin).id ], readers: [])
+    assert_equal 1, book.accesses.size
+  end
+end