diff --git a/spec/models/ticket/number/date_spec.rb b/spec/models/ticket/number/date_spec.rb
new file mode 100644
index 000000000..f97cb04e5
--- /dev/null
+++ b/spec/models/ticket/number/date_spec.rb
@@ -0,0 +1,86 @@
+require 'rails_helper'
+
+RSpec.describe Ticket::Number::Date do
+  describe '.generate' do
+    let(:number) { described_class.generate }
+
+    before { travel_to(Time.zone.parse('1955-11-05')) }
+
+    context 'with a "ticket_number_date" setting with checksum: false (default)' do
+      context 'and a single-digit system_id' do
+        before { Setting.set('system_id', 1) }
+
+        it 'returns a string following the pattern date + system_id + zero-padded number' do
+          expect(number).to eq('1955110510001')
+        end
+      end
+
+      context 'and a two-digit system_id' do
+        before { Setting.set('system_id', 88) }
+
+        it 'returns a string following the pattern date + system_id + zero-padded number' do
+          expect(number).to eq('19551105880001')
+        end
+      end
+    end
+
+    context 'with a "ticket_number_date" setting with checksum: true' do
+      before { Setting.set('ticket_number_date', { checksum: true }) }
+
+      context 'and a single-digit system_id' do
+        before { Setting.set('system_id', 1) }
+
+        it 'returns a string following the pattern date + system_id + zero-padded number + checksum' do
+          expect(number).to eq('19551105100012')
+        end
+      end
+
+      context 'and a two-digit system_id' do
+        before { Setting.set('system_id', 88) }
+
+        it 'returns a string following the pattern date + system_id + zero-padded number + checksum' do
+          expect(number).to eq('195511058800012')
+        end
+      end
+    end
+  end
+
+  describe '.check' do
+    context 'for tickets with date-style numbers' do
+      let(:ticket) { create(:ticket, number: ticket_number) }
+      let(:ticket_number) { "19551105#{Setting.get('system_id')}0001" }
+      let(:check_query) { ticket.subject_build(ticket.title) }
+
+      context 'when system_id is the same as when ticket was created' do
+        before do
+          Setting.set('system_id', 1)
+          ticket  # create ticket
+        end
+
+        it 'returns the ticket matching the number in the given string' do
+          expect(described_class.check(check_query)).to eq(ticket)
+        end
+      end
+
+      context 'when system_id is different from when ticket was created' do
+        before do
+          Setting.set('system_id', 1)
+          ticket  # create ticket
+          Setting.set('system_id', 999)
+        end
+
+        it 'returns nil' do
+          expect(described_class.check(check_query)).to be(nil)
+        end
+
+        context 'and "ticket_number_ignore_system_id" is true' do
+          before { Setting.set('ticket_number_ignore_system_id', true) }
+
+          it 'returns the ticket matching the number in the given string' do
+            expect(described_class.check(check_query)).to eq(ticket)
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/spec/models/ticket/number/increment_spec.rb b/spec/models/ticket/number/increment_spec.rb
new file mode 100644
index 000000000..899a4fd99
--- /dev/null
+++ b/spec/models/ticket/number/increment_spec.rb
@@ -0,0 +1,114 @@
+require 'rails_helper'
+
+RSpec.describe Ticket::Number::Increment do
+  describe '.generate' do
+    let(:number) { described_class.generate }
+    let(:system_id) { Setting.get('system_id') }
+    let(:ticket_count) { Ticket::Counter.find_by(generator: 'Increment').content }
+
+    context 'with a "ticket_number_increment" setting with...' do
+      context 'min_size: 5' do
+        before { Setting.set('ticket_number_increment', { min_size: 5 }) }
+
+        it 'returns a 5-character string' do
+          expect(number).to be_a(String)
+          expect(number.length).to be(5)
+        end
+
+        context 'when "system_id" setting exceeds :min_size' do
+          before { Setting.set('system_id', 123_456) }
+
+          it 'still adheres to numbering pattern (and does not require padding zeroes)' do
+            expect(number).to match(/^#{system_id}#{ticket_count}$/)
+          end
+        end
+
+        it 'returns a string following the pattern system_id + padding zeroes + ticket_count' do
+          expect(number).to match(/^#{system_id}0*#{ticket_count}$/)
+        end
+
+        context '/ checksum: false (default)' do
+          before { Setting.set('ticket_number_increment', { min_size: 5, checksum: false }) }
+
+          it 'returns a 5-character string' do
+            expect(number).to be_a(String)
+            expect(number.length).to be(5)
+          end
+
+          it 'returns a string following the pattern system_id + padding zeroes + ticket_counter' do
+            expect(number).to match(/^#{system_id}0*#{ticket_count}$/)
+          end
+
+          context 'when "system_id" setting exceeds :min_size' do
+            before { Setting.set('system_id', 123_456) }
+
+            it 'still adheres to numbering pattern (and does not require padding zeroes)' do
+              expect(number).to match(/^#{system_id}#{ticket_count}$/)
+            end
+          end
+        end
+
+        context '/ checksum: true' do
+          before { Setting.set('ticket_number_increment', { min_size: 5, checksum: true }) }
+
+          it 'returns a 5-character string' do
+            expect(number).to be_a(String)
+            expect(number).to eq(number.to_i.to_s)
+            expect(number.length).to be(5)
+          end
+
+          it 'returns a string following the pattern system_id + padding zeroes + ticket_counter + checksum' do
+            expect(number).to match(/^#{system_id}0*#{ticket_count}\d$/)
+          end
+
+          context 'when "system_id" setting exceeds :min_size' do
+            before { Setting.set('system_id', 123_456) }
+
+            it 'still adheres to numbering pattern (and does not require padding zeroes)' do
+              expect(number).to match(/^#{system_id}#{ticket_count}\d$/)
+            end
+          end
+        end
+      end
+    end
+  end
+
+  describe '.check' do
+    context 'for tickets with increment-style numbers' do
+      let(:ticket) { create(:ticket, number: ticket_number) }
+      let(:ticket_number) { "#{Setting.get('system_id')}0001" }
+      let(:check_query) { ticket.subject_build(ticket.title) }
+
+      context 'when system_id is the same as when ticket was created' do
+        before do
+          Setting.set('system_id', 1)
+          ticket  # create ticket
+        end
+
+        it 'returns the ticket matching the number in the given string' do
+          expect(described_class.check(check_query)).to eq(ticket)
+        end
+      end
+
+      context 'when system_id is different from when ticket was created' do
+        before do
+          Setting.set('system_id', 1)
+          ticket  # create ticket
+          Setting.set('system_id', 999)
+        end
+
+        it 'returns nil' do
+          expect(described_class.check(check_query)).to be(nil)
+        end
+
+        context 'and "ticket_number_ignore_system_id" is true' do
+          before { Setting.set('ticket_number_ignore_system_id', true) }
+
+          it 'returns the ticket matching the number in the given string' do
+            expect(described_class.check(check_query)).to eq(ticket)
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/spec/models/ticket/number_spec.rb b/spec/models/ticket/number_spec.rb
new file mode 100644
index 000000000..7c28108f1
--- /dev/null
+++ b/spec/models/ticket/number_spec.rb
@@ -0,0 +1,36 @@
+require 'rails_helper'
+
+RSpec.describe Ticket::Number do
+  let(:stubbed_subclass) { double('Foo') }
+
+  before { stub_const('Ticket::Number::Foo', stubbed_subclass)  }
+
+  describe '.generate' do
+    before { Setting.set('ticket_number', 'Ticket::Number::Foo') }
+
+    it 'defers to subclass specified in "ticket_number" setting' do
+      expect(Ticket::Number::Foo).to receive(:generate)
+      expect(described_class.generate).to be(nil)
+    end
+  end
+
+  describe '.check' do
+    before { Setting.set('ticket_number', 'Ticket::Number::Foo') }
+
+    it 'defers to subclass specified in "ticket_number" setting' do
+      expect(Ticket::Number::Foo).to receive(:check).with('foo')
+      expect(described_class.check('foo')).to be(nil)
+    end
+  end
+
+  describe '.adapter' do
+    it 'defaults to Ticket::Number::Increment' do
+      expect(described_class.adapter).to be(Ticket::Number::Increment)
+    end
+
+    it 'depends on "ticket_number" setting' do
+      expect { Setting.set('ticket_number', 'Ticket::Number::Foo') }
+        .to change(described_class, :adapter).to(Ticket::Number::Foo)
+    end
+  end
+end
diff --git a/test/unit/ticket_number_test.rb b/test/unit/ticket_number_test.rb
deleted file mode 100644
index d97cca3f0..000000000
--- a/test/unit/ticket_number_test.rb
+++ /dev/null
@@ -1,166 +0,0 @@
-require 'test_helper'
-
-class TicketNumberTest < ActiveSupport::TestCase
-  test 'number' do
-    Setting.set('ticket_number_increment', { checksum: false, min_size: 5 })
-    Setting.set('system_id', 1)
-
-    number = Ticket::Number.generate
-    assert_equal(number.to_s.length, 5)
-
-    Setting.set('ticket_number_increment', { checksum: false, min_size: 10 })
-    Setting.set('system_id', 1)
-
-    number = Ticket::Number.generate
-    assert_equal(number.to_s.length, 10)
-
-    Setting.set('ticket_number_increment', { checksum: true, min_size: 5 })
-    Setting.set('system_id', 1)
-
-    number = Ticket::Number.generate
-    assert_equal(number.to_s.length, 5)
-
-    Setting.set('ticket_number_increment', { checksum: true, min_size: 10 })
-    Setting.set('system_id', 1)
-
-    number = Ticket::Number.generate
-    assert_equal(number.to_s.length, 10)
-
-    Setting.set('ticket_number_increment', { checksum: false, min_size: 5 })
-    Setting.set('system_id', 88)
-
-    number = Ticket::Number.generate
-    assert_equal(number.to_s.length, 5)
-
-    Setting.set('ticket_number_increment', { checksum: false, min_size: 10 })
-    Setting.set('system_id', 88)
-
-    number = Ticket::Number.generate
-    assert_equal(number.to_s.length, 10)
-
-    Setting.set('ticket_number_increment', { checksum: true, min_size: 5 })
-    Setting.set('system_id', 88)
-
-    number = Ticket::Number.generate
-    assert_equal(number.to_s.length, 5)
-
-    Setting.set('ticket_number_increment', { checksum: true, min_size: 10 })
-    Setting.set('system_id', 88)
-
-    number = Ticket::Number.generate
-    assert_equal(number.to_s.length, 10)
-
-    150.times do
-      number = Ticket::Number.generate
-      assert_equal(number.to_s.length, 10)
-    end
-
-  end
-
-  test 'number check' do
-    Setting.set('ticket_number_increment', { checksum: false, min_size: 5 })
-
-    Setting.set('system_id', 1)
-
-    ticket = Ticket.create!(
-      title:         'test 1',
-      group:         Group.lookup(name: 'Users'),
-      customer_id:   2,
-      state:         Ticket::State.lookup(name: 'new'),
-      priority:      Ticket::Priority.lookup(name: '2 normal'),
-      updated_by_id: 1,
-      created_by_id: 1,
-    )
-    subject = ticket.subject_build(ticket.title)
-
-    ticket_check = Ticket::Number.check(subject)
-    assert_equal(ticket.id, ticket_check.id)
-
-    Setting.set('system_id', 999)
-
-    ticket_check = Ticket::Number.check(subject)
-    assert_not(ticket_check)
-
-    Setting.set('ticket_number_ignore_system_id', true)
-
-    ticket_check = Ticket::Number.check(subject)
-    assert_equal(ticket.id, ticket_check.id)
-  end
-
-  test 'date' do
-    Setting.set('ticket_number', 'Ticket::Number::Date')
-    Setting.set('ticket_number_date', { checksum: false })
-    Setting.set('system_id', 1)
-    system_id = Setting.get('system_id')
-    number_prefix = "#{Time.zone.now.strftime('%Y%m%d')}#{system_id}"
-
-    number = Ticket::Number.generate
-    assert_equal(number.to_s.length, 13)
-    assert_match(/#{number_prefix}/, number.to_s)
-
-    Setting.set('ticket_number_date', { checksum: false })
-    Setting.set('system_id', 88)
-
-    number = Ticket::Number.generate
-    system_id = Setting.get('system_id')
-    number_prefix = "#{Time.zone.now.strftime('%Y%m%d')}#{system_id}"
-    assert_equal(number.to_s.length, 14)
-    assert_match(/#{number_prefix}/, number.to_s)
-
-    Setting.set('ticket_number_date', { checksum: true })
-    Setting.set('system_id', 1)
-
-    number = Ticket::Number.generate
-    system_id = Setting.get('system_id')
-    number_prefix = "#{Time.zone.now.strftime('%Y%m%d')}#{system_id}"
-    assert_equal(number.to_s.length, 14)
-    assert_match(/#{number_prefix}/, number.to_s)
-
-    Setting.set('ticket_number_date', { checksum: true })
-    Setting.set('system_id', 88)
-
-    number = Ticket::Number.generate
-    system_id = Setting.get('system_id')
-    number_prefix = "#{Time.zone.now.strftime('%Y%m%d')}#{system_id}"
-    assert_equal(number.to_s.length, 15)
-    assert_match(/#{number_prefix}/, number.to_s)
-
-    150.times do
-      number = Ticket::Number.generate
-      assert_equal(number.to_s.length, 15)
-    end
-
-  end
-
-  test 'date check' do
-    Setting.set('ticket_number', 'Ticket::Number::Date')
-    Setting.set('ticket_number_date', { checksum: false })
-
-    Setting.set('system_id', 1)
-
-    ticket = Ticket.create!(
-      title:         'test 1',
-      group:         Group.lookup(name: 'Users'),
-      customer_id:   2,
-      state:         Ticket::State.lookup(name: 'new'),
-      priority:      Ticket::Priority.lookup(name: '2 normal'),
-      updated_by_id: 1,
-      created_by_id: 1,
-    )
-    subject = ticket.subject_build(ticket.title)
-
-    ticket_check = Ticket::Number.check(subject)
-    assert_equal(ticket.id, ticket_check.id)
-
-    Setting.set('system_id', 999)
-
-    ticket_check = Ticket::Number.check(subject)
-    assert_not(ticket_check)
-
-    Setting.set('ticket_number_ignore_system_id', true)
-
-    ticket_check = Ticket::Number.check(subject)
-    assert_equal(ticket.id, ticket_check.id)
-  end
-
-end