Specify basic behaviour of Sequel truncation

Connecting to the databases using the same details used in ActiveRecord tests
(at least for now) so that configuration is in only one place -- verifying
compliance with the new Sequel specs won't need existing developers (or CI
systems) to change their process.

Existing behaviour (bugs and all) are verified for the major supported Sequel
connection adapters:

  * postgres
  * sqlite
  * mysql
  * mysql2

Verifying the compliance for other adapters (or the same ones with different
configuration parameters) should be very easy -- just another line.

spec/database_cleaner/sequel/truncation_spec.rb

@@ -3,11 +3,142 @@ require 'database_cleaner/sequel/truncation'
 require 'database_cleaner/shared_strategy'
 require 'sequel'
 
+# XXX: use ActiveRecord's db_config (`db/config.yml`) for CI/dev convenience
+require 'support/active_record/database_setup'
+
 module DatabaseCleaner
   module Sequel
     describe Truncation do
       it_should_behave_like "a generic strategy"
       it_should_behave_like "a generic truncation strategy"
     end
+
+    shared_examples 'a Sequel truncation strategy' do
+
+      # XXX: it'd be really nice if Truncation accepted db: constructor parameter
+      let(:truncation) do
+        t = Truncation.new
+        t.db = db
+        t
+      end
+
+      context 'when several tables have data' do
+        before(:each) do
+          db.create_table!(:precious_stones) { primary_key :id }
+          db.create_table!(:replaceable_trifles)  { primary_key :id }
+          db.create_table!(:worthless_junk)  { primary_key :id }
+
+          db[:precious_stones].insert
+          db[:replaceable_trifles].insert
+          db[:worthless_junk].insert
+        end
+        context 'by default' do
+          it 'truncates all the tables' do
+            t = Truncation.new
+            t.db = db
+            t.clean
+
+            expect(db[:replaceable_trifles]).to have(0).rows
+            expect(db[:worthless_junk]).to have(0).rows
+            expect(db[:precious_stones]).to have(0).rows
+          end
+        end
+        context 'when the Truncation is restricted to "only: [...]" some tables' do
+          it 'truncates only the mentioned tables (and leaves the rest alone)' do
+            t = Truncation.new(only: ['worthless_junk', 'replaceable_trifles'])
+            t.db = db
+            t.clean
+
+            expect(db[:replaceable_trifles]).to have(0).rows
+            expect(db[:worthless_junk]).to have(0).rows
+            expect(db[:precious_stones]).to have(1).rows
+          end
+        end
+        context 'when the Truncation is restricted to "except: [...]" some tables' do
+          it 'leaves the mentioned tables alone (and truncates the rest)' do
+            t = Truncation.new(except: ['precious_stones']) # XXX: Strings only, symbols are ignored
+            t.db = db
+            t.clean
+
+            expect(db[:replaceable_trifles]).to be_empty
+            expect(db[:worthless_junk]).to be_empty
+            expect(db[:precious_stones]).to have(1).item
+          end
+        end
+      end
+    end
+
+    shared_examples_for 'a truncation strategy without autoincrement resets' do
+      it "leaves AUTO_INCREMENT index alone by default (BUG: it should be reset instead)" do
+        # Jordan Hollinger made everything reset auto increment IDs
+        # in commit 6a0104382647e5c06578aeac586c0333c8944492 so I'm pretty sure
+        # everything is meant to reset by default.
+        #
+        # For Postgres, db[:mytable].truncate(restart: true) should work.
+        # For SQLite, db[:sqlite_sequence].where(name: 'mytable').delete
+
+        db.create_table!(:replaceable_trifles) { primary_key :id }
+        table = db[:replaceable_trifles]
+        2.times { table.insert }
+
+        truncation.clean
+
+        id_after_clean = table.insert
+        pending('the bug being fixed') do
+          expect(id_after_clean).to eq 1
+        end
+      end
+      # XXX: it'd be really nice if Truncation accepted db: constructor parameter
+      let(:truncation) do
+        t = Truncation.new
+        t.db = db
+        t
+      end
+    end
+
+    shared_examples_for 'a truncation strategy that resets autoincrement keys by default' do
+      it "resets AUTO_INCREMENT primary keys" do
+        db.create_table!(:replaceable_trifles) { primary_key :id }
+        table = db[:replaceable_trifles]
+        2.times { table.insert }
+
+        truncation.clean
+
+        id_after_clean = table.insert
+        expect(id_after_clean).to eq 1
+      end
+
+      # XXX: it'd be really nice if Truncation accepted db: constructor parameter
+      let(:truncation) do
+        t = Truncation.new
+        t.db = db
+        t
+      end
+    end
+
+    half_supported_configurations = [
+      {url: 'sqlite:///',   connection_options: db_config['sqlite3']},
+      {url: 'postgres:///', connection_options: db_config['postgres']},
+    ]
+    supported_configurations = [
+      {url: 'mysql:///',    connection_options: db_config['mysql']},
+      {url: 'mysql2:///',   connection_options: db_config['mysql2']}
+    ]
+    supported_configurations.each do |config|
+      describe "Sequel truncation (using a #{config[:url]} connection)" do
+        let(:db) { ::Sequel.connect(config[:url], config[:connection_options]) }
+
+        it_behaves_like 'a Sequel truncation strategy'
+        it_behaves_like 'a truncation strategy that resets autoincrement keys by default'
+      end
+    end
+    half_supported_configurations.each do |config|
+      describe "Sequel truncation (using a #{config[:url]} connection)" do
+        let(:db) { ::Sequel.connect(config[:url], config[:connection_options]) }
+
+        it_behaves_like 'a Sequel truncation strategy'
+        it_behaves_like 'a truncation strategy without autoincrement resets'
+      end
+    end
   end
 end