spec: make specs resilient to pre-existing records, refs SD-1570

in jenkins-land we've historically used db snapshots so the db will be
empty. but if you `rake db:migrate` your test db, you'll have things like
default accounts, notifications, etc., which can break certain specs

Change-Id: I175e651d1b50671e630dc0181d1c4d25e78abe97
Reviewed-on: https://gerrit.instructure.com/95249
Reviewed-by: Landon Wilkins <lwilkins@instructure.com>
Product-Review: Landon Wilkins <lwilkins@instructure.com>
QA-Review: Landon Wilkins <lwilkins@instructure.com>
Tested-by: Jenkins

spec/spec_helper.rb

@@ -60,19 +60,15 @@ module WebMock::API
   end
 end
 
-# ensure people aren't creating records outside the rspec lifecycle, e.g.
-# inside a describe/context block rather than a let/before/example
+# nuke the db (say, if `rake db:migrate RAILS_ENV=test` created records),
+# and then ensure people aren't creating records outside the rspec
+# lifecycle, e.g. inside a describe/context block rather than a
+# let/before/example
 require_relative 'support/blank_slate_protection'
-BlankSlateProtection.enable!
+BlankSlateProtection.install!
 
 require_relative 'support/discourage_slow_specs'
 
-RSpec::Core::ExampleGroup.singleton_class.prepend(Module.new {
-  def run_examples(*)
-    BlankSlateProtection.disable { super }
-  end
-})
-
 Dir[Rails.root.join("spec/support/**/*.rb")].each { |f| require f }
 
 ActionView::TestCase::TestController.view_paths = ApplicationController.view_paths

spec/support/blank_slate_protection.rb

@@ -1,28 +1,36 @@
 require_relative "./call_stack_utils"
 
 module BlankSlateProtection
-  def create_or_update
-    return super unless BlankSlateProtection.enabled?
-    return super if caller.grep(BlankSlateProtection.exempt_patterns).present?
+  module ActiveRecord
+    def create_or_update
+      return super unless BlankSlateProtection.enabled?
+      return super if caller.grep(BlankSlateProtection.exempt_patterns).present?
 
-    location = CallStackUtils.best_line_for(caller).sub(/:in .*/, '')
-    if caller.grep(/_context_hooks/).present?
-      $stderr.puts "\e[31mError: Don't create records inside `:all` hooks!"
-      $stderr.puts "See: " + location + "\e[0m"
+      location = CallStackUtils.best_line_for(caller).sub(/:in .*/, '')
+      if caller.grep(/_context_hooks/).present?
+        $stderr.puts "\e[31mError: Don't create records inside `:all` hooks!"
+        $stderr.puts "See: " + location + "\e[0m"
+        $stderr.puts
+        $stderr.puts "\e[33mTIP:\e[0m change this to `:each`, or if you are really concerned"
+        $stderr.puts "about performance, use `:once`. `:all` hooks are dangerous because"
+        $stderr.puts "they can leave around garbage that affects later specs"
+      else
+        $stderr.puts "\e[31mError: Don't create records outside the rspec lifecycle!"
+        $stderr.puts "See: " + location + "\e[0m"
+        $stderr.puts
+        $stderr.puts "\e[33mTIP:\e[0m move this into a `before`, `let` or `it`. Otherwise it will exist"
+        $stderr.puts "before *any* specs start, and possibly be deleted/modified before the"
+        $stderr.puts "spec that needs it actually runs."
+      end
       $stderr.puts
-      $stderr.puts "\e[33mTIP:\e[0m change this to `:each`, or if you are really concerned"
-      $stderr.puts "about performance, use `:once`. `:all` hooks are dangerous because"
-      $stderr.puts "they can leave around garbage that affects later specs"
-    else
-      $stderr.puts "\e[31mError: Don't create records outside the rspec lifecycle!"
-      $stderr.puts "See: " + location + "\e[0m"
-      $stderr.puts
-      $stderr.puts "\e[33mTIP:\e[0m move this into a `before`, `let` or `it`. Otherwise it will exist"
-      $stderr.puts "before *any* specs start, and possibly be deleted/modified before the"
-      $stderr.puts "spec that needs it actually runs."
+      exit! 1
+    end
+  end
+
+  module ExampleGroup
+    def run_examples(*)
+      BlankSlateProtection.disable { super }
     end
-    $stderr.puts
-    exit! 1
   end
 
   # switchman and once-ler have special snowflake context hooks where data
@@ -34,26 +42,51 @@ module BlankSlateProtection
       @enabled
     end
 
-    def enable!
+    def install!
+      truncate_all_tables!
+      ::RSpec::Core::ExampleGroup.singleton_class.prepend ExampleGroup
+      ::ActiveRecord::Base.include ActiveRecord
       @enabled = true
     end
 
-    def disable!
-      @enabled = false
-    end
-
     def disable
-      enabled = @enabled
-      disable!
+      @enabled = false
       yield
     ensure
-      @enabled = enabled
+      @enabled = true
     end
 
     def exempt_patterns
       Regexp.new(EXEMPT_PATTERNS.map { |pattern| Regexp.escape(pattern) }.join("|"))
     end
+
+    def get_table_names(connection)
+      # use custom SQL to exclude tables from extensions
+      schema = connection.shard.name if connection.instance_variable_get(:@config)[:use_qualified_names]
+      table_names = connection.query(<<-SQL, 'SCHEMA').map(&:first)
+         SELECT relname
+         FROM pg_class INNER JOIN pg_namespace ON relnamespace=pg_namespace.oid
+         WHERE nspname = #{schema ? "'#{schema}'" : 'ANY (current_schemas(false))'}
+           AND relkind='r'
+           AND NOT EXISTS (
+             SELECT 1 FROM pg_depend WHERE deptype='e' AND objid=pg_class.oid
+           )
+      SQL
+      table_names.delete('schema_migrations')
+      table_names
+    end
+
+    def truncate_all_tables!(quick: true)
+      return if quick && Account.all.empty? # this is the most likely table to have stuff
+      puts "truncating all tables..."
+      Shard.with_each_shard do
+        model_connections = ::ActiveRecord::Base.descendants.map(&:connection).uniq
+        model_connections.each do |connection|
+          table_names = get_table_names(connection)
+          next if table_names.empty?
+          connection.execute("TRUNCATE TABLE #{table_names.map { |t| connection.quote_table_name(t) }.join(',')}")
+        end
+      end
+    end
   end
 end
-
-ActiveRecord::Base.include BlankSlateProtection