rake corrupts development database

Question

When I run rake to run specific/all test(s), it corrupts development database.

I verified that db for each environment is different.

database.yml

postgre_common_config: &postgre_common_config
  adapter: postgresql
  encoding: unicode
  pool: 5
  username: postgres # if using default PostgreSQL user then the value should be: postgres
  password: postgres
  host: localhost

development:
  database: mag_development
  <<: *postgre_common_config

test:
  database: mag_test
  <<: *postgre_common_config

production:
  database: mag_production
  <<: *postgre_common_config

test_helper.rb

ENV['RAILS_ENV'] = 'test'
require File.expand_path('../../config/environment', __FILE__)
require 'rails/test_help'

class ActiveSupport::TestCase
  fixtures :all
end

This is really annoying as it takes lot of time to prepare data to test specific feature manually. Please help.