Fix prepared statements disabled test again

- Due to `assert_nothing_raised` this test was not really testing
  anything.
- So updated it to assert that the query gives expected result.
- Also in general we can use `connection.unprepared_statement` for
  testing queries w/o prepared statements but it can't be used in this
  case. This test cases was added because when prepared_statements
  config is set to false, then DetermineIfPreparableVisitor module
  does not extended by Arel visitor resulting into an error. Ref: https://github.com/rails/rails/pull/22748.
- Because DetermineIfPreparableVisitor module does not get added to the
  visitor chain only if prepared_statements is false while **setting up
  connection**, not when `unprepared_statement` is used.
- I have also added an assertion for making sure that prepared_config
  is set to false from the start, so that nobody accidentally removes
  the connection setup using `arunit_without_prepared_statements` and
  replaces it with stubs or unprepared_statement.

activerecord/test/cases/adapters/postgresql/prepared_statements_disabled_test.rb

@@ -0,0 +1,25 @@
+require "cases/helper"
+require "models/computer"
+require "models/developer"
+
+class PreparedStatementsDisabledTest < ActiveRecord::PostgreSQLTestCase
+  fixtures :developers
+
+  def setup
+    @conn = ActiveRecord::Base.establish_connection :arunit_without_prepared_statements
+  end
+
+  def teardown
+    @conn.release_connection
+    ActiveRecord::Base.establish_connection :arunit
+  end
+
+  def test_select_query_works_even_when_prepared_statements_are_disabled
+    assert_not Developer.connection.prepared_statements
+
+    david = developers(:david)
+
+    assert_equal david, Developer.where(name: "David").last # With Binds
+    assert_operator Developer.count, :>, 0 # Without Binds
+  end
+end

activerecord/test/cases/adapters/postgresql/prepared_statements_test.rb

@@ -1,22 +0,0 @@
-require "cases/helper"
-require "models/computer"
-require "models/developer"
-
-class PreparedStatementsTest < ActiveRecord::PostgreSQLTestCase
-  fixtures :developers
-
-  def setup
-    @conn = ActiveRecord::Base.establish_connection :arunit_without_prepared_statements
-  end
-
-  def teardown
-    @conn.release_connection
-    ActiveRecord::Base.establish_connection :arunit
-  end
-
-  def test_nothing_raised_with_falsy_prepared_statements
-    assert_nothing_raised do
-      Developer.where(id: 1).to_a
-    end
-  end
-end