autodetect available strategies so we don't need to repeat ourselves, and narrow the ORM Adapter API further.

ADAPTERS.md

@@ -50,9 +50,9 @@ The file structure you end up with will look something like this
 #### orm_name.rb
 
 File `orm_name.rb` **must** do the following:
-  * define module method `.available_strategies` on DatabaseCleaner::OrmName.
-  * require all the gems strategies
-  * configure DatabaseCleaner with the default strategy for the ORM.
+  * require `database_cleaner-core`
+  * require all the strategies
+  * configure `DatabaseCleaner` with the default strategy for the ORM.
 
 So, in the end you will end up with a file that might look something like this:
 
@@ -65,14 +65,6 @@ require 'database_cleaner/orm_name/transaction'
 require 'database_cleaner/orm_name/truncation'
 require 'database_cleaner/orm_name/deletion'
 
-module DatabaseCleaner
-  module OrmName
-    def self.available_strategies
-      %i[transaction truncation deletion]
-    end
-  end
-end
-
 DatabaseCleaner[:orm_name].strategy = :transaction
 ```
 

lib/database_cleaner/cleaner.rb

@@ -7,6 +7,12 @@ module DatabaseCleaner
   class UnknownStrategySpecified < ArgumentError; end
 
   class Cleaner
+    def self.available_strategies(orm_module)
+      # introspect publically available constants to get list of strategies, leaving out common but obviously non-strategy constants.
+      # if you're writing an adapter and this method is finding a constant in it that is not a valid strategy, consider making it private with Module#private_constant.
+      (orm_module.constants - [:Base, :VERSION]).map(&:downcase)
+    end
+
     include Comparable
 
     def <=>(other)
@@ -79,7 +85,8 @@ module DatabaseCleaner
       strategy_module_name = strategy.to_s.capitalize
       orm_module.const_get(strategy_module_name)
     rescue NameError
-      raise UnknownStrategySpecified, "The '#{strategy}' strategy does not exist for the #{orm} ORM!  Available strategies: #{orm_module.available_strategies.join(', ')}"
+      available_strategies = self.class.available_strategies(orm_module)
+      raise UnknownStrategySpecified, "The '#{strategy}' strategy does not exist for the #{orm} ORM!  Available strategies: #{available_strategies.join(', ')}"
     end
 
     def orm_module

lib/database_cleaner/spec/shared_examples.rb

@@ -1,3 +1,5 @@
+require "database_cleaner/cleaner"
+
 RSpec.shared_examples_for "a database_cleaner strategy" do
   it { is_expected.to respond_to(:db)  }
   it { is_expected.to respond_to(:db=)  }
@@ -7,10 +9,8 @@ RSpec.shared_examples_for "a database_cleaner strategy" do
 end
 
 RSpec.shared_examples_for "a database_cleaner adapter" do
-  it { expect(described_class).to respond_to(:available_strategies) }
-
   describe 'all strategies should adhere to a database_cleaner strategy interface' do
-    described_class.available_strategies.each do |strategy|
+    DatabaseCleaner::Cleaner.available_strategies(described_class).each do |strategy|
       subject { described_class.const_get(strategy.to_s.capitalize).new }
 
       it_behaves_like 'a database_cleaner strategy'

spec/database_cleaner/cleaner_spec.rb

@@ -118,15 +118,16 @@ module DatabaseCleaner
       subject(:cleaner) { Cleaner.new(:active_record) }
 
       let(:strategy_class) { Class.new }
+      let(:orm_module) { Module.new }
 
       before do
-        orm_module = Module.new do
-          def self.available_strategies
-            %i[truncation transaction deletion]
-          end
-        end
         stub_const "DatabaseCleaner::ActiveRecord", orm_module
         stub_const "DatabaseCleaner::ActiveRecord::Truncation", strategy_class
+        # stub consts that shouldn't show up in strategy list
+        stub_const "DatabaseCleaner::ActiveRecord::VERSION", "2.0.0"
+        stub_const "DatabaseCleaner::ActiveRecord::Base", Module.new
+        stub_const "DatabaseCleaner::ActiveRecord::Helpers", Module.new
+        orm_module.private_constant :Helpers
       end
 
       it "should look up and create a the named strategy for the current ORM" do
@@ -159,7 +160,7 @@ module DatabaseCleaner
 
       it "raises UnknownStrategySpecified on a bad strategy, and lists available strategies" do
         expect { cleaner.strategy = :horrible_plan }.to \
-          raise_error(UnknownStrategySpecified, "The 'horrible_plan' strategy does not exist for the active_record ORM!  Available strategies: truncation, transaction, deletion")
+          raise_error(UnknownStrategySpecified, "The 'horrible_plan' strategy does not exist for the active_record ORM!  Available strategies: truncation")
       end
     end