Add method_call_assertions and use them instead of Mocha

Six Mocha calls prove quite resistant to Minitestification. For example,
if we replace

```
  ActiveRecord::Associations::HasManyAssociation
    .any_instance
    .expects(:reader)
    .never
```

with `assert_not_called`, Minitest wisely raises

```
NameError: undefined method `reader' for class `ActiveRecord::Associations::HasManyAssociation'
```

as `:reader` comes from a deeply embedded abstract class,
`ActiveRecord::Associations::CollectionAssociation`.

This patch tackles this difficulty by adding
`ActiveSupport::Testing::MethodCallAsserts#assert_called_on_instance_of`
which injects a stubbed method into `klass`, and verifies the number of
times it is called, similar to `assert_called`. It also adds  a convenience
method, `assert_not_called_on_instance_of`, mirroring
`assert_not_called`.

It uses the new method_call_assertions to replace the remaining Mocha
calls in `ActiveRecord` tests.

[utilum + bogdanvlviv + kspath]

1 files changed, 3 insertions, 2 deletions

diff --git a/activerecord/test/cases/associations/eager_test.rb b/activerecord/test/cases/associations/eager_test.rb
index 5b8d4722af..a1fba8dc66 100644
--- a/activerecord/test/cases/associations/eager_test.rb
+++ b/activerecord/test/cases/associations/eager_test.rb
@@ -1571,8 +1571,9 @@ class EagerAssociationTest < ActiveRecord::TestCase
 
   # CollectionProxy#reader is expensive, so the preloader avoids calling it.
   test "preloading has_many_through association avoids calling association.reader" do
-    ActiveRecord::Associations::HasManyAssociation.any_instance.expects(:reader).never
-    Author.preload(:readonly_comments).first!
+    assert_not_called_on_instance_of(ActiveRecord::Associations::HasManyAssociation, :reader) do
+      Author.preload(:readonly_comments).first!
+    end
   end
 
   test "preloading through a polymorphic association doesn't require the association to exist" do