diff --git a/test/test_assets_compiler.rb b/test/test_assets_compiler.rb
new file mode 100644
index 0000000..c1806c8
--- /dev/null
+++ b/test/test_assets_compiler.rb
@@ -0,0 +1,115 @@
+require 'minitest/autorun'
+require 'prism'
+require 'tmpdir'
+require 'fileutils'
+
+class AssetsCompilerTest < Minitest::Test
+  def test_compiles_files_into_content_addressed_names
+    with_source do |source, output|
+      write(source, 'application.css', 'body { color: red; }')
+
+      manifest = Prism::Assets::Compiler.new(source: source, output: output).compile!
+
+      fingerprinted = manifest.lookup('application.css')
+      assert_match(/\Aapplication-[0-9a-f]{8}\.css\z/, fingerprinted)
+      assert_equal 'body { color: red; }', File.read(File.join(output, fingerprinted))
+    end
+  end
+
+  def test_same_content_produces_the_same_fingerprint_across_compiles
+    with_source do |source, output|
+      write(source, 'app.js', 'console.log(1);')
+      compiler = Prism::Assets::Compiler.new(source: source, output: output)
+
+      first = compiler.compile!.lookup('app.js')
+      second = compiler.compile!.lookup('app.js')
+
+      assert_equal first, second
+    end
+  end
+
+  def test_changed_content_produces_a_different_fingerprint
+    with_source do |source, output|
+      write(source, 'app.js', 'console.log(1);')
+      compiler = Prism::Assets::Compiler.new(source: source, output: output)
+      first = compiler.compile!.lookup('app.js')
+
+      write(source, 'app.js', 'console.log(2);')
+      second = compiler.compile!.lookup('app.js')
+
+      refute_equal first, second
+    end
+  end
+
+  def test_stale_fingerprinted_files_are_removed_on_recompile
+    with_source do |source, output|
+      write(source, 'app.js', 'console.log(1);')
+      compiler = Prism::Assets::Compiler.new(source: source, output: output)
+      old_fingerprinted = compiler.compile!.lookup('app.js')
+      old_path = File.join(output, old_fingerprinted)
+      assert File.file?(old_path)
+
+      write(source, 'app.js', 'console.log(2);')
+      compiler.compile!
+
+      refute File.file?(old_path), 'stale fingerprinted file should have been cleaned up'
+    end
+  end
+
+  def test_unchanged_files_are_left_alone_when_a_sibling_changes
+    with_source do |source, output|
+      write(source, 'a.css', 'a')
+      write(source, 'b.css', 'b')
+      compiler = Prism::Assets::Compiler.new(source: source, output: output)
+      first = compiler.compile!
+      a_fingerprint = first.lookup('a.css')
+
+      write(source, 'b.css', 'b-changed')
+      second = compiler.compile!
+
+      assert_equal a_fingerprint, second.lookup('a.css')
+      assert File.file?(File.join(output, a_fingerprint))
+    end
+  end
+
+  def test_preserves_subdirectory_structure_as_logical_paths
+    with_source do |source, output|
+      write(source, 'css/nested/theme.css', '.x{}')
+
+      manifest = Prism::Assets::Compiler.new(source: source, output: output).compile!
+
+      fingerprinted = manifest.lookup('css/nested/theme.css')
+      assert_match(%r{\Acss/nested/theme-[0-9a-f]{8}\.css\z}, fingerprinted)
+      assert File.file?(File.join(output, fingerprinted))
+    end
+  end
+
+  def test_writes_manifest_json_to_the_output_directory
+    with_source do |source, output|
+      write(source, 'a.css', 'a')
+      Prism::Assets::Compiler.new(source: source, output: output).compile!
+
+      manifest_path = File.join(output, 'manifest.json')
+      assert File.file?(manifest_path)
+      parsed = JSON.parse(File.read(manifest_path))
+      assert_match(/\Aa-[0-9a-f]{8}\.css\z/, parsed['a.css'])
+    end
+  end
+
+  private
+
+  def with_source
+    Dir.mktmpdir do |root|
+      source = File.join(root, 'source')
+      output = File.join(root, 'output')
+      FileUtils.mkdir_p(source)
+      yield source, output
+    end
+  end
+
+  def write(source, relative, content)
+    path = File.join(source, relative)
+    FileUtils.mkdir_p(File.dirname(path))
+    File.write(path, content)
+  end
+end
diff --git a/test/test_assets_manifest.rb b/test/test_assets_manifest.rb
new file mode 100644
index 0000000..15ea035
--- /dev/null
+++ b/test/test_assets_manifest.rb
@@ -0,0 +1,43 @@
+require 'minitest/autorun'
+require 'prism'
+require 'tmpdir'
+
+class AssetsManifestTest < Minitest::Test
+  def test_lookup_returns_the_fingerprinted_path
+    manifest = Prism::Assets::Manifest.new('application.css' => 'application-deadbeef.css')
+    assert_equal 'application-deadbeef.css', manifest.lookup('application.css')
+  end
+
+  def test_lookup_accepts_symbol_or_string
+    manifest = Prism::Assets::Manifest.new('application.css' => 'application-deadbeef.css')
+    assert_equal 'application-deadbeef.css', manifest.lookup(:'application.css')
+  end
+
+  def test_lookup_raises_on_unknown_asset
+    manifest = Prism::Assets::Manifest.new
+    error = assert_raises(Prism::Assets::Manifest::AssetNotFound) { manifest.lookup('missing.css') }
+    assert_match(/missing\.css/, error.message)
+  end
+
+  def test_key_predicate
+    manifest = Prism::Assets::Manifest.new('a.js' => 'a-11111111.js')
+    assert manifest.key?('a.js')
+    refute manifest.key?('b.js')
+  end
+
+  def test_save_and_load_round_trip
+    Dir.mktmpdir do |dir|
+      path = File.join(dir, 'manifest.json')
+      original = Prism::Assets::Manifest.new('a.css' => 'a-cafef00d.css', 'b.js' => 'b-0ff1ce00.js')
+      original.save(path)
+
+      loaded = Prism::Assets::Manifest.load(path)
+      assert_equal original.to_h, loaded.to_h
+    end
+  end
+
+  def test_load_of_missing_file_returns_an_empty_manifest
+    manifest = Prism::Assets::Manifest.load('/no/such/manifest.json')
+    refute manifest.key?('anything.css')
+  end
+end