Collections automatically cache and fetch partials.

Collections can take advantage of `multi_read` if they render one template
and their partials begin with a cache call.

The cache call must correspond to either what the collections elements are
rendered as, or match the inferred name of the partial.

So with a notifications/_notification.html.erb template like:

```ruby
<% cache notification %>
  <%# ... %>
<% end %>
```

A collection would be able to use `multi_read` if rendered like:

```ruby
<%= render @notifications %>
<%= render partial: 'notifications/notification', collection: @notifications, as: :notification %>
```

2 files changed, 7 insertions, 0 deletions

diff --git a/actionpack/test/fixtures/customers/_commented_customer.html.erb b/actionpack/test/fixtures/customers/_commented_customer.html.erb
new file mode 100644
index 0000000000..d5f6e3b491
--- /dev/null
+++ b/actionpack/test/fixtures/customers/_commented_customer.html.erb
@@ -0,0 +1,4 @@
+<%# I'm a comment %>
+<% cache customer do %>
+  <%= customer.name %>, <%= customer.id %>
+<% end %>
\ No newline at end of file
diff --git a/actionpack/test/fixtures/customers/_customer.html.erb b/actionpack/test/fixtures/customers/_customer.html.erb
new file mode 100644
index 0000000000..67e9f6d411
--- /dev/null
+++ b/actionpack/test/fixtures/customers/_customer.html.erb
@@ -0,0 +1,3 @@
+<% cache customer do %>
+  <%= customer.name %>, <%= customer.id %>
+<% end %>
\ No newline at end of file