diff --git a/test/test_flash.rb b/test/test_flash.rb
new file mode 100644
index 0000000..c54a286
--- /dev/null
+++ b/test/test_flash.rb
@@ -0,0 +1,69 @@
+require 'minitest/autorun'
+require 'prism'
+
+class FlashTest < Minitest::Test
+  def test_set_value_is_not_visible_in_same_flash_read_before_sweep
+    session = Prism::Params.new
+    flash = Prism::Flash.new(session)
+    flash[:notice] = 'saved'
+    assert_nil flash[:notice], 'value set this request should not be readable via [] until next request'
+  end
+
+  def test_sweep_persists_pending_values_into_session
+    session = Prism::Params.new
+    flash = Prism::Flash.new(session)
+    flash[:notice] = 'saved'
+    flash.sweep
+    assert_equal({ 'notice' => 'saved' }, session['_flash'])
+  end
+
+  def test_next_request_reads_previous_pending_value
+    session = Prism::Params.new
+    first = Prism::Flash.new(session)
+    first[:notice] = 'saved'
+    first.sweep
+
+    second = Prism::Flash.new(session)
+    assert_equal 'saved', second[:notice]
+  end
+
+  def test_flash_does_not_carry_over_a_second_time
+    session = Prism::Params.new
+    first = Prism::Flash.new(session)
+    first[:notice] = 'saved'
+    first.sweep
+
+    second = Prism::Flash.new(session)
+    second[:notice]
+    second.sweep
+
+    third = Prism::Flash.new(session)
+    assert_nil third[:notice]
+  end
+
+  def test_now_reads_current_flash_without_waiting_for_sweep
+    session = Prism::Params.new
+    session['_flash'] = { 'notice' => 'saved' }
+    flash = Prism::Flash.new(session)
+    assert_equal 'saved', flash.now[:notice]
+  end
+
+  def test_keep_carries_current_flash_into_next_request
+    session = Prism::Params.new
+    session['_flash'] = { 'notice' => 'saved' }
+    flash = Prism::Flash.new(session)
+    flash.keep
+    flash.sweep
+
+    next_flash = Prism::Flash.new(session)
+    assert_equal 'saved', next_flash[:notice]
+  end
+
+  def test_empty_predicate
+    session = Prism::Params.new
+    flash = Prism::Flash.new(session)
+    assert flash.empty?
+    session['_flash'] = { 'notice' => 'x' }
+    assert Prism::Flash.new(session).empty? == false
+  end
+end
diff --git a/test/test_session.rb b/test/test_session.rb
new file mode 100644
index 0000000..bce4212
--- /dev/null
+++ b/test/test_session.rb
@@ -0,0 +1,33 @@
+require 'minitest/autorun'
+require 'prism'
+
+class SessionTest < Minitest::Test
+  def test_roundtrip
+    cookie = Prism::Session.encode({ 'user' => 'foksiu', 'count' => 3 }, 'top-secret')
+    decoded = Prism::Session.decode(cookie, 'top-secret')
+    assert_equal 'foksiu', decoded['user']
+    assert_equal 3, decoded['count']
+  end
+
+  def test_tampering_rejected
+    cookie = Prism::Session.encode({ 'admin' => false }, 'top-secret')
+    payload, signature = cookie.split('--', 2)
+    forged = "#{payload}--#{'0' * signature.size}"
+    assert_equal({}, Prism::Session.decode(forged, 'top-secret'))
+  end
+
+  def test_wrong_secret
+    cookie = Prism::Session.encode({ 'x' => 1 }, 'secret-a')
+    assert_equal({}, Prism::Session.decode(cookie, 'secret-b'))
+  end
+
+  def test_cookie_is_url_safe
+    cookie = Prism::Session.encode({ 'blob' => 'a' * 60 }, 's')
+    assert_nil cookie[/[^A-Za-z0-9_\-]/], "expected url safe cookie, got: #{cookie}"
+  end
+
+  def test_missing_cookie
+    assert_equal({}, Prism::Session.decode(nil, 's'))
+    assert_equal({}, Prism::Session.decode('', 's'))
+  end
+end
diff --git a/test/test_template.rb b/test/test_template.rb
new file mode 100644
index 0000000..d75f916
--- /dev/null
+++ b/test/test_template.rb
@@ -0,0 +1,29 @@
+require 'minitest/autorun'
+require 'prism'
+
+class TemplateTest < Minitest::Test
+  def test_interpolation
+    assert_equal 'Hello, Ruby!', Prism::Template.render('Hello, <%= name %>!', name: 'Ruby')
+  end
+
+  def test_html_escape
+    result = Prism::Template.render('<%= value %>', value: '<script>alert(1)</script>')
+    assert_equal '&lt;script&gt;alert(1)&lt;/script&gt;', result
+  end
+
+  def test_raw_output
+    result = Prism::Template.render('<%== value %>', value: '<b>bold</b>')
+    assert_equal '<b>bold</b>', result
+  end
+
+  def test_logic
+    template = '<% items.each do |n| %><%= n %>;<% end %>'
+    assert_equal '1;2;3;', Prism::Template.render(template, items: [1, 2, 3])
+  end
+
+  def test_conditional
+    template = '<% if admin %>yes<% else %>no<% end %>'
+    assert_equal 'yes', Prism::Template.render(template, admin: true)
+    assert_equal 'no', Prism::Template.render(template, admin: false)
+  end
+end
diff --git a/test/test_view.rb b/test/test_view.rb
new file mode 100644
index 0000000..c76f0e5
--- /dev/null
+++ b/test/test_view.rb
@@ -0,0 +1,55 @@
+require 'minitest/autorun'
+require 'prism'
+require 'tmpdir'
+require 'fileutils'
+
+class ViewTest < Minitest::Test
+  def setup
+    @dir = Dir.mktmpdir('prism-view')
+    FileUtils.mkdir_p(File.join(@dir, 'posts'))
+    FileUtils.mkdir_p(File.join(@dir, 'layouts'))
+    File.write(File.join(@dir, 'posts', 'index.erb'), '<%= greeting %>')
+    File.write(File.join(@dir, 'posts', '_item.erb'), '[<%= label %>]')
+    File.write(File.join(@dir, 'layouts', 'application.erb'), 'before-<%== content %>-after')
+    @view = Prism::View.new(@dir)
+  end
+
+  def teardown
+    FileUtils.remove_entry(@dir)
+  end
+
+  def test_render_reads_and_evaluates_template
+    assert_equal 'hi', @view.render('posts/index', locals: { greeting: 'hi' })
+  end
+
+  def test_render_wraps_content_with_layout
+    result = @view.render('posts/index', locals: { greeting: 'hi' }, layout: :application)
+    assert_equal 'before-hi-after', result
+  end
+
+  def test_render_partial_directly
+    assert_equal '[x]', @view.render_partial('posts/item', locals: { label: 'x' })
+  end
+
+  def test_partial_called_from_within_a_template_resolves_relative_to_it
+    File.write(File.join(@dir, 'posts', 'index.erb'), "<%== partial('item', locals: { label: greeting }) %>")
+    assert_equal '[hi]', @view.render('posts/index', locals: { greeting: 'hi' })
+  end
+
+  def test_render_collection_exposes_item_and_counter_locals
+    File.write(File.join(@dir, 'posts', '_item.erb'), '<%= label_counter %>:<%= label %>;')
+    result = @view.render_collection('posts/item', %w[a b], as: :label)
+    assert_equal '1:a;2:b;', result
+  end
+
+  def test_render_collection_defaults_local_name_to_partial_basename
+    File.write(File.join(@dir, 'posts', '_item.erb'), '<%= item %>;')
+    result = @view.render_collection('posts/item', %w[a b])
+    assert_equal 'a;b;', result
+  end
+
+  def test_missing_template_raises_a_descriptive_error
+    error = assert_raises(Prism::View::TemplateNotFound) { @view.render('posts/missing') }
+    assert_includes error.message, 'posts/missing'
+  end
+end