Remove unnecessary Mocha stubs

[utilum]

Step 1 in #33162

While modifying tests to replace use of Mocha it became evident that some calls to Mocha#stub and Mocha#stubs do not have any impact on the test case. The same is true of some calls to returns on such objects. This patch removes both.

I speculate that the setup for one test was sometimes copied from onto another without verifying necessity. Tracing each of these instances to its origins and determining the moment it became unnecessary is fascinating, but a lot of work.

For example, @connection = stub("Connection", create_database: true) was introduced six years ago as part of quite a refactoring. I'd need a whole new stack to verify it was necessary at the time, and it's gone through several changes since.

So I did not complete the historical research.

[rails-bot]

r? @schneems

(@rails-bot has picked a reviewer for you, use r? to override)

[bogdanvlviv]

I also found few unnecessary Mocha stubs on the current branch.
Let's apply it too and see if the tests fail
here is diff:

diff --git a/activerecord/test/cases/tasks/mysql_rake_test.rb b/activerecord/test/cases/tasks/mysql_rake_test.rb
index 6cddfaefeb..d39122d9ef 100644
--- a/activerecord/test/cases/tasks/mysql_rake_test.rb
+++ b/activerecord/test/cases/tasks/mysql_rake_test.rb
@@ -77,7 +77,6 @@ def test_create_when_database_exists_outputs_info_to_stderr

     class MysqlDBCreateWithInvalidPermissionsTest < ActiveRecord::TestCase
       def setup
-        @connection    = stub("Connection", create_database: true)
         @error         = Mysql2::Error.new("Invalid permissions")
         @configuration = {
           "adapter"  => "mysql2",
@@ -86,7 +85,6 @@ def setup
           "password" => "wossname"
         }

-        ActiveRecord::Base.stubs(:connection).returns(@connection)
         ActiveRecord::Base.stubs(:establish_connection).raises(@error)

         $stdout, @original_stdout = StringIO.new, $stdout
diff --git a/activerecord/test/cases/tasks/postgresql_rake_test.rb b/activerecord/test/cases/tasks/postgresql_rake_test.rb
index 6be929d1af..2f41f6a556 100644
--- a/activerecord/test/cases/tasks/postgresql_rake_test.rb
+++ b/activerecord/test/cases/tasks/postgresql_rake_test.rb
@@ -141,7 +141,6 @@ def setup
         }

         ActiveRecord::Base.stubs(:connection).returns(@connection)
-        ActiveRecord::Base.stubs(:clear_active_connections!).returns(true)
         ActiveRecord::Base.stubs(:establish_connection).returns(true)
       end

@@ -219,7 +218,6 @@ def test_db_retrieves_collation

     class PostgreSQLStructureDumpTest < ActiveRecord::TestCase
       def setup
-        @connection    = stub(schema_search_path: nil, structure_dump: true)
         @configuration = {
           "adapter"  => "postgresql",
           "database" => "my-app-db"
@@ -355,7 +353,6 @@ def with_structure_dump_flags(flags)

     class PostgreSQLStructureLoadTest < ActiveRecord::TestCase
       def setup
-        @connection    = stub
         @configuration = {
           "adapter"  => "postgresql",
           "database" => "my-app-db"
diff --git a/activerecord/test/cases/tasks/sqlite_rake_test.rb b/activerecord/test/cases/tasks/sqlite_rake_test.rb
index 0594e304e3..c9e7badf76 100644
--- a/activerecord/test/cases/tasks/sqlite_rake_test.rb
+++ b/activerecord/test/cases/tasks/sqlite_rake_test.rb
@@ -45,8 +45,6 @@ def test_db_create_when_file_exists
       end

       def test_db_create_with_file_does_nothing
-        File.stubs(:exist?).returns(true)
-
         ActiveRecord::Base.expects(:establish_connection).never

         ActiveRecord::Tasks::DatabaseTasks.create @configuration, "/rails/root"

[utilum]

Looks good! Thank you.

[kaspth]

Why are these stubs not needed? Were they never needed?

Can you elaborate a bit about how you found out they weren't needed in your commit message?

Thanks for working on this, both of you!

[utilum]

Following @bogdanvlviv 's additional deletions, I rescanned the code and found several more such cases. Just pushed.