Extended tests coverage for SE instance

Tested that we correctly pass arguments down to the
methods of an extension instance.

app/assets/javascripts/editor/source_editor_instance.js

@@ -73,9 +73,7 @@ export default class EditorInstance {
         if (methodExtension) {
           const extension = extensionsStore.get(methodExtension);
 
-          return (...args) => {
-            return extension.api[prop].call(seInstance, ...args, receiver);
-          };
+          return (...args) => extension.api[prop].call(seInstance, receiver, ...args);
         }
         return Reflect.get(seInstance[prop] ? seInstance : target, prop, receiver);
       },

spec/frontend/editor/helpers.js

-export class MyClassExtension {
+export class SEClassExtension {
   // eslint-disable-next-line class-methods-use-this
   provides() {
     return {
@@ -8,7 +8,7 @@ export class MyClassExtension {
   }
 }
 
-export function MyFnExtension() {
+export function SEFnExtension() {
   return {
     fnExtMethod: () => 'fn own method',
     provides: () => {
@@ -19,7 +19,7 @@ export function MyFnExtension() {
   };
 }
 
-export const MyConstExt = () => {
+export const SEConstExt = () => {
   return {
     provides: () => {
       return {
@@ -29,6 +29,33 @@ export const MyConstExt = () => {
   };
 };
 
+export function SEWithSetupExt() {
+  return {
+    onSetup: (setupOptions = {}, instance) => {
+      if (setupOptions && !Array.isArray(setupOptions)) {
+        Object.entries(setupOptions).forEach(([key, value]) => {
+          Object.assign(instance, {
+            [key]: value,
+          });
+        });
+      }
+    },
+    provides: () => {
+      return {
+        returnInstanceAndProps: (instance, stringProp, objProp = {}) => {
+          return [stringProp, objProp, instance];
+        },
+        returnInstance: (instance) => {
+          return instance;
+        },
+        giveMeContext: () => {
+          return this;
+        },
+      };
+    },
+  };
+}
+
 export const conflictingExtensions = {
   WithInstanceExt: () => {
     return {

spec/frontend/editor/source_editor_extension_spec.js

@@ -22,15 +22,15 @@ describe('Editor Extension', () => {
 
   it.each`
     definition                  | setupOptions | expectedName
-    ${helpers.MyClassExtension} | ${undefined} | ${'MyClassExtension'}
-    ${helpers.MyClassExtension} | ${{}}        | ${'MyClassExtension'}
-    ${helpers.MyClassExtension} | ${dummyObj}  | ${'MyClassExtension'}
-    ${helpers.MyFnExtension}    | ${undefined} | ${'MyFnExtension'}
-    ${helpers.MyFnExtension}    | ${{}}        | ${'MyFnExtension'}
-    ${helpers.MyFnExtension}    | ${dummyObj}  | ${'MyFnExtension'}
-    ${helpers.MyConstExt}       | ${undefined} | ${'MyConstExt'}
-    ${helpers.MyConstExt}       | ${{}}        | ${'MyConstExt'}
-    ${helpers.MyConstExt}       | ${dummyObj}  | ${'MyConstExt'}
+    ${helpers.SEClassExtension} | ${undefined} | ${'SEClassExtension'}
+    ${helpers.SEClassExtension} | ${{}}        | ${'SEClassExtension'}
+    ${helpers.SEClassExtension} | ${dummyObj}  | ${'SEClassExtension'}
+    ${helpers.SEFnExtension}    | ${undefined} | ${'SEFnExtension'}
+    ${helpers.SEFnExtension}    | ${{}}        | ${'SEFnExtension'}
+    ${helpers.SEFnExtension}    | ${dummyObj}  | ${'SEFnExtension'}
+    ${helpers.SEConstExt}       | ${undefined} | ${'SEConstExt'}
+    ${helpers.SEConstExt}       | ${{}}        | ${'SEConstExt'}
+    ${helpers.SEConstExt}       | ${dummyObj}  | ${'SEConstExt'}
   `(
     'correctly creates extension for definition = $definition and setupOptions = $setupOptions',
     ({ definition, setupOptions, expectedName }) => {
@@ -51,9 +51,9 @@ describe('Editor Extension', () => {
   describe('api', () => {
     it.each`
       definition                  | expectedKeys
-      ${helpers.MyClassExtension} | ${['shared', 'classExtMethod']}
-      ${helpers.MyFnExtension}    | ${['fnExtMethod']}
-      ${helpers.MyConstExt}       | ${['constExtMethod']}
+      ${helpers.SEClassExtension} | ${['shared', 'classExtMethod']}
+      ${helpers.SEFnExtension}    | ${['fnExtMethod']}
+      ${helpers.SEConstExt}       | ${['constExtMethod']}
     `('correctly returns API for $definition', ({ definition, expectedKeys }) => {
       const extension = new EditorExtension({ definition });
       const expectedApi = Object.fromEntries(