Add test coverage for turbo-frame[busy]

During the request lifecycle, `<turbo-frame>` elements will toggle the
`[busy]` boolean attribute to true when the request starts, and then
remove it when the request ends.

This commit adds functional test coverage for that behavior.

src/core/frames/frame_controller.ts

@@ -178,7 +178,8 @@ export class FrameController implements AppearanceObserverDelegate, FetchRequest
   // Form submission delegate
 
   formSubmissionStarted(formSubmission: FormSubmission) {
-
+    const frame = this.findFrameElement(formSubmission.formElement)
+    frame.setAttribute("busy", "")
   }
 
   formSubmissionSucceededWithResponse(formSubmission: FormSubmission, response: FetchResponse) {
@@ -195,7 +196,8 @@ export class FrameController implements AppearanceObserverDelegate, FetchRequest
   }
 
   formSubmissionFinished(formSubmission: FormSubmission) {
-
+    const frame = this.findFrameElement(formSubmission.formElement)
+    frame.removeAttribute("busy")
   }
 
   // View delegate

src/tests/fixtures/form.html

@@ -115,10 +115,15 @@
     </div>
     <hr>
     <div id="targets-frame">
-      <form action="/__turbo/redirect" method="post" data-turbo-frame="frame">
+      <form action="/__turbo/redirect" method="post" data-turbo-frame="frame" class="one">
         <input type="hidden" name="path" value="/src/tests/fixtures/one.html">
         <button type="submit">Submit</button>
       </form>
+
+      <form action="/__turbo/redirect" method="post" data-turbo-frame="frame" class="frame">
+        <input type="hidden" name="path" value="/src/tests/fixtures/frames/frame.html">
+        <button type="submit">Submit</button>
+      </form>
     </div>
     <turbo-frame id="frame">
       <h2>Frame: Form</h2>

src/tests/fixtures/test.js

@@ -10,6 +10,15 @@
     eventLogs.push([event.type, event.detail])
   }
 
+  window.mutationLogs = []
+
+  new MutationObserver((mutations) => {
+    for (const { attributeName, oldValue, target } of mutations.filter(({ type }) => type == "attributes")) {
+      if (target instanceof HTMLElement) {
+        mutationLogs.push([attributeName, target.id, target.getAttribute(attributeName)])
+      }
+    }
+  }).observe(document, { subtree: true, childList: true, attributes: true })
 })([
   "turbo:before-cache",
   "turbo:before-render",

src/tests/functional/form_submission_tests.ts

@@ -185,6 +185,23 @@ export class FormSubmissionTests extends TurboDriveTestCase {
     this.assert.equal(await this.attributeForSelector("#frame", "src"), url.href, "redirects the target frame")
   }
 
+  async "test frame form submission toggles the ancestor frame's [busy] attribute"() {
+    await this.clickSelector("#frame form.redirect input[type=submit]")
+
+    this.assert.equal(await this.nextAttributeMutationNamed("frame", "busy"), "", "sets [busy] on the #frame")
+    this.assert.equal(await this.nextAttributeMutationNamed("frame", "busy"), null, "removes [busy] from the #frame")
+  }
+
+  async "test frame form submission toggles the target frame's [busy] attribute"() {
+    await this.clickSelector('#targets-frame form.frame [type="submit"]')
+
+    this.assert.equal(await this.nextAttributeMutationNamed("frame", "busy"), "", "sets [busy] on the #frame")
+
+    const title = await this.querySelector("#frame h2")
+    this.assert.equal(await title.getVisibleText(), "Frame: Loaded")
+    this.assert.equal(await this.nextAttributeMutationNamed("frame", "busy"), null, "removes [busy] from the #frame")
+  }
+
   async "test frame form submission with empty created response"() {
     const htmlBefore = await this.outerHTMLForSelector("#frame")
     const button = await this.querySelector("#frame form.created input[type=submit]")
@@ -292,7 +309,7 @@ export class FormSubmissionTests extends TurboDriveTestCase {
 
   async "test form submission targets disabled frame"() {
     this.remote.execute(() => document.getElementById("frame")?.setAttribute("disabled", ""))
-    await this.clickSelector('#targets-frame [type="submit"]')
+    await this.clickSelector('#targets-frame form.one [type="submit"]')
     await this.nextBody
 
     this.assert.equal(await this.pathname, "/src/tests/fixtures/one.html")

src/tests/functional/frame_tests.ts

@@ -25,6 +25,13 @@ export class FrameTests extends TurboDriveTestCase {
     this.assert.equal(otherEvents.length, 0, "no more events")
   }
 
+  async "test following a link driving a frame toggles the [busy] attribute"() {
+    await this.clickSelector("#hello a")
+
+    this.assert.equal(await this.nextAttributeMutationNamed("frame", "busy"), "", "sets [busy] on the #frame")
+    this.assert.equal(await this.nextAttributeMutationNamed("frame", "busy"), null, "removes [busy] from the #frame")
+  }
+
   async "test following a link to a page without a matching frame results in an empty frame"() {
     await this.clickSelector("#missing a")
     await this.nextBeat

src/tests/helpers/turbo_drive_test_case.ts

@@ -3,9 +3,11 @@ import { RemoteChannel } from "./remote_channel"
 import { Element } from "@theintern/leadfoot"
 
 type EventLog = [string, any]
+type MutationLog = [string, string, string | null]
 
 export class TurboDriveTestCase extends FunctionalTestCase {
   eventLogChannel: RemoteChannel<EventLog> = new RemoteChannel(this.remote, "eventLogs")
+  mutationLogChannel: RemoteChannel<MutationLog> = new RemoteChannel(this.remote, "mutationLogs")
   lastBody?: Element
 
   async beforeTest() {
@@ -33,6 +35,15 @@ export class TurboDriveTestCase extends FunctionalTestCase {
     return record[1]
   }
 
+  async nextAttributeMutationNamed(elementId: string, attributeName: string): Promise<string | null> {
+    let record: MutationLog | undefined
+    while (!record) {
+      const records = await this.mutationLogChannel.read(1)
+      record = records.find(([attribute, id]) => id == elementId && attribute == attributeName)
+    }
+    return record[2]
+  }
+
   get nextBody(): Promise<Element> {
     return (async () => {
       let body