diff --git a/test/models/plugin_test.rb b/test/models/plugin_test.rb
new file mode 100644
index 0000000..1dc6558
--- /dev/null
+++ b/test/models/plugin_test.rb
@@ -0,0 +1,144 @@
+require "test_helper"
+
+class PluginTest < ActiveSupport::TestCase
+  setup do
+    @plugin = FactoryBot.build(:plugin)
+  end
+
+  sub_test_case ".installed" do
+    setup do
+      gem_list = <<-GEM_LIST.strip_heredoc
+        dummy (3.3.3)
+        fluent-plugin-foo (0.1.2)
+        more_dummy (0.0.1)
+      GEM_LIST
+      stub(FluentGem).gem { "gem" }
+      stub(FluentGem).__double_definition_create__.call(:`, "gem list 2>&1") { gem_list }
+      @target = Plugin.new(gem_name: "fluent-plugin-foo", version: "0.1.2")
+    end
+
+    test "detect foo plugin" do
+      assert_equal(@target.inspect, Plugin.installed.first.inspect)
+    end
+
+    test "detected foo plugin is marked as installed" do
+      assert do
+        @target.installed?
+      end
+    end
+
+    test "detected foo plugin version to be installed_version" do
+      assert_equal(@target.version, @target.installed_version)
+    end
+  end
+
+  sub_test_case "#valid?" do
+    data("nil is invalid" => [nil, false],
+         "something filled is valid" => ["foobar", true])
+    test "gem_name" do |(name, is_valid)|
+      @plugin.gem_name = name
+      assert_equal(is_valid, @plugin.valid?)
+    end
+
+    data("nil is invalid" => [nil, false],
+         "something filled is valid" => ["0.0.1", true])
+    test "version" do |(version, is_valid)|
+      @plugin.version = version
+      assert_equal(is_valid, @plugin.valid?)
+    end
+  end
+
+  sub_test_case "#install!" do
+    def install_plugin(is_valid, is_installed)
+      stub(@plugin).valid? { is_valid }
+      stub(@plugin).installed? { is_installed }
+      @plugin.install!
+    end
+
+
+    data("installed" => [true, 0],
+         "not installed" => [false, 1])
+    test "valid" do |(is_installed, n)|
+      mock(FluentGem).install(anything, "--no-ri", "--no-rdoc", "-v", anything).times(n) {}
+      install_plugin(true, is_installed)
+    end
+
+    data("installed" => [true, :install],
+         "not installed" => [false, :installed])
+    test "invalid" do |(is_installed, method)|
+      mock(FluentGem).__send__(method).times(0)
+      install_plugin(false, is_installed)
+    end
+
+    test "system command error" do
+      stub(FluentGem).gem { "gem" }
+      mock(FluentGem).system("gem", "install", "fluent-plugin-dummy", "--no-ri", "--no-rdoc", "-v", "1.2.3").at_least(1) { false }
+      assert_raise(FluentGem::GemError.new("failed command: `gem install fluent-plugin-dummy --no-ri --no-rdoc -v 1.2.3`")) do
+        @plugin.install!
+      end
+    end
+  end
+
+  data("installed" => [true, 1],
+       "uninstalled" => [false, 0])
+  test "#uninstall!" do |(is_installed, n)|
+    installed_plugin = FactoryBot.build(:plugin, gem_name: "fluent-plugin-foobar")
+    mock(installed_plugin).installed? { is_installed }
+    mock(installed_plugin).gem_uninstall.times(n) {}
+    installed_plugin.uninstall!
+  end
+
+  test "#upgrade!" do
+    installed_plugin = FactoryBot.build(:plugin, gem_name: "fluent-plugin-foobar", version: "1.0.0")
+    stub(installed_plugin).installed? { true }
+    stub(FluentGem).gem { "gem" }
+    stub(FluentGem).run("gem", "install", "fluent-plugin-foobar", "--no-ri", "--no-rdoc", "-v", "1.2.0") { true }
+    mock(installed_plugin).uninstall! {}
+    mock(FluentGem).install("fluent-plugin-foobar", "--no-ri", "--no-rdoc", "-v", "1.2.0") {}
+    installed_plugin.upgrade!("1.2.0")
+  end
+
+  test "#to_param" do
+    assert do
+      @plugin.to_param == @plugin.gem_name
+    end
+  end
+
+  sub_test_case "Gem version" do
+    setup do
+      @plugin = FactoryBot.build(:plugin, version: "1.0.0")
+      @versions = %w(1.0.1 0.99.1 1.0.0 0.99.0 0.1.0 0.0.3 0.0.2 0.0.1)
+      @authors = %w(foo bar)
+      json_response = @versions.map do |version|
+        {
+          number: version,
+          summary: "summary of #{version}",
+          authors: @authors
+        }
+      end.to_json
+      stub_request(:get, @plugin.gem_json_url).to_return(body: json_response)
+    end
+
+    test "latest version is 1.0.0" do
+      assert_equal("1.0.1", @plugin.latest_version)
+    end
+
+    test "1.0.0 is not lates" do
+      assert do
+        !@plugin.latest_version?
+      end
+    end
+
+    test "released_versions is sorted" do
+      assert_equal(@versions.sort_by{|ver| Gem::Version.new(ver) }.reverse, @plugin.released_versions)
+    end
+
+    test "authors" do
+      assert_equal(@authors, @plugin.authors)
+    end
+
+    test "summary" do
+      assert_equal("summary of #{@plugin.version}", @plugin.summary)
+    end
+  end
+end