DEV: improves sk api (#9653)

- reduces the API to 3 actions for now: appendContent/prependContent/onChange
- well tested
- removes all previous APIS which were only half supported or too dangerous as they could collide with other plugins or core behaviors
- this plugins also puts every sk test helpers in one file

test/javascripts/helpers/select-kit-helper.js

@@ -276,3 +276,38 @@ export default function selectKit(selector) {
     }
   };
 }
+
+export function testSelectKitModule(moduleName, options = {}) {
+  moduleForComponent(`select-kit/${moduleName}`, {
+    integration: true,
+
+    beforeEach() {
+      this.set("subject", selectKit());
+      options.beforeEach && options.beforeEach.call(this);
+    },
+
+    afterEach() {
+      options.afterEach && options.afterEach.call(this);
+    }
+  });
+}
+
+export const DEFAULT_CONTENT = [
+  { id: 1, name: "foo" },
+  { id: 2, name: "bar" },
+  { id: 3, name: "baz" }
+];
+
+export function setDefaultState(ctx, value, options = {}) {
+  const properties = Object.assign(
+    {
+      value,
+      onChange: v => {
+        ctx.set("value", v);
+      }
+    },
+    options || {}
+  );
+
+  ctx.setProperties(properties);
+}