test(kiosk): manifest, identity, version and client unit tests

- TestReadIdentity: literal, const, chained, cross-package, alias,
  other-module and Requires shapes; refusals naming ID()/Requires()
- TestDerive, TestManifestFormat, TestCheck, TestVersions,
  TestRegistryClient (httptest: escaping, 404, envelopes, cap, redirect)
- runnable ExampleMarshal and ExampleNewestCompatible
- party TestDescribe: copy of the plugin list, publish once per app

modules/kiosk/example_test.go

@@ -0,0 +1,57 @@
+package kiosk_test
+
+import (
+	"fmt"
+
+	"git.golem15.com/golem15/summercms/modules/kiosk"
+)
+
+// Marshal writes the plugin.yaml bytes: the generated header, the fields
+// in a fixed order and the required plugins sorted by ID.
+func ExampleMarshal() {
+	out, err := kiosk.Marshal(kiosk.Manifest{
+		Schema:      kiosk.SchemaVersion,
+		ID:          "acme.shop",
+		Module:      "example.test/sm-shop-plugin",
+		Package:     "example.test/sm-shop-plugin",
+		Name:        "Shop",
+		Description: "Products, carts and orders.",
+		Framework:   "v0.6.0",
+		Requires:    kiosk.Requires{"acme.user": "v0.1.2", "acme.payment": ""},
+	})
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	fmt.Print(string(out))
+	// Output:
+	// # Generated by summer plugin:manifest. Do not edit; rerun the command.
+	// schema: 1
+	// id: acme.shop
+	// module: example.test/sm-shop-plugin
+	// package: example.test/sm-shop-plugin
+	// name: Shop
+	// description: Products, carts and orders.
+	// framework: v0.6.0
+	// requires:
+	//   acme.payment: ""
+	//   acme.user: v0.1.2
+}
+
+// NewestCompatible picks the newest release whose framework minimum the
+// application's framework meets; the list order does not matter.
+func ExampleNewestCompatible() {
+	versions := []kiosk.RegistryVersion{
+		{Version: "v0.3.0", Framework: "v0.7.0"},
+		{Version: "v0.2.1", Framework: "v0.6.0"},
+		{Version: "v0.1.0", Framework: "v0.5.0"},
+	}
+	for _, framework := range []string{"v0.6.2", "v0.7.0", "v0.4.0"} {
+		v, ok := kiosk.NewestCompatible(versions, framework)
+		fmt.Println(framework, v.Version, ok)
+	}
+	// Output:
+	// v0.6.2 v0.2.1 true
+	// v0.7.0 v0.3.0 true
+	// v0.4.0  false
+}