Deprecate this.get and this.set on test contexts

text/1188-deprecate-get-set-test-context.md

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+---
+stage: accepted
+start-date: 2026-06-22T00:00:00.000Z
+release-date:
+release-versions:
+teams:
+  - framework
+  - learning
+  - typescript
+prs:
+  accepted: # update this to the PR that you propose your RFC in
+project-link:
+---
+
+# Deprecate `this.get` and `this.set` on Test Contexts
+
+## Summary
+
+Deprecate the use of `this.get` and `this.set` on the test context object in rendering tests, as a logical conclusion of [RFC #785](https://github.com/emberjs/rfcs/blob/master/text/0785-remove-set-get-in-tests.md), which introduced `render(component)` and `rerender()` as the modern replacements.
+
+## Motivation
+
+RFC #785 introduced two new testing utilities — an updated `render` helper that accepts a component directly, and a new `rerender()` function — specifically to remove the need for `this.get` and `this.set` in rendering tests. Those APIs shipped in Ember v4.5.0 and are now the recommended approach for writing rendering tests.
+
+The legacy pattern of setting values on `this` in a rendering test was problematic for several reasons laid out in RFC #785:
+
+1. **Inconsistency with application code.** In post-Octane Ember, `get` and `set` are unnecessary; properties are tracked natively. Requiring them in tests is a confusing holdover.
+
+2. **Incorrect rendering semantics.** `this.set` in tests is run-wrapped, causing a synchronous full DOM flush on every call. This does not reflect how Ember schedules DOM updates in production code, where changes to tracked state are coalesced.
+
+3. **TypeScript friction.** Assigning arbitrary properties to `this` forces developers to redeclare the `TestContext` interface for every test module, causing leakage of property declarations across tests and defeating the purpose of static type checking.
+
+Now that the modern replacements have been stable for multiple major versions, it is appropriate to deprecate the old approach and eventually remove it, completing the migration to a cleaner and more accurate testing model.
+
+## Transition Path
+
+### Before (deprecated)
+
+```js
+import { render } from '@ember/test-helpers';
+import { hbs } from 'ember-cli-htmlbars';
+
+test('it renders the name', async function (assert) {
+  this.set('name', 'Zoey');
+
+  await render(hbs`<MyComponent @name={{this.name}} />`);
+
+  assert.dom('[data-test-name]').hasText(this.get('name'));
+
+  this.set('name', 'Tomster');
+
+  assert.dom('[data-test-name]').hasText(this.get('name'));
+});
+```
+
+### After (recommended)
+
+```js
+import { render, rerender } from '@ember/test-helpers';
+import { tracked } from '@glimmer/tracking';
+
+test('it renders the name', async function (assert) {
+  const state = new class {
+    @tracked name = 'Zoey';
+  };
+
+  await render(<template><MyComponent @name={{state.name}} /></template>);
+
+  assert.dom('[data-test-name]').hasText('Zoey');
+
+  state.name = 'Tomster';
+  await rerender();
+
+  assert.dom('[data-test-name]').hasText('Tomster');
+});
+```
+
+For projects that have not yet adopted `<template>` tag syntax, `precompileTemplate` from `@ember/template-compilation` can be used together with a scope hash instead:
+
+```js
+import { render, rerender } from '@ember/test-helpers';
+import { precompileTemplate } from '@ember/template-compilation';
+import { tracked } from '@glimmer/tracking';
+
+test('it renders the name', async function (assert) {
+  const state = new class {
+    @tracked name = 'Zoey';
+  };
+
+  await render(precompileTemplate('<MyComponent @name={{state.name}} />', {
+    scope: () => ({ state, MyComponent }),
+  }));
+
+  assert.dom('[data-test-name]').hasText('Zoey');
+
+  state.name = 'Tomster';
+  await rerender();
+
+  assert.dom('[data-test-name]').hasText('Tomster');
+});
+```
+
+### Deprecation message
+
+When `this.set` or `this.get` is called on the test context, `@ember/test-helpers` should emit a deprecation warning of the form:
+
+```
+Using `this.set` / `this.get` on the test context is deprecated.
+Please migrate to passing a component or template with a local tracked state object to `render()`,
+and use `rerender()` to await DOM updates.
+See https://deprecations.emberjs.com/id/test-context-get-set for details.
+```
+
+### Ecosystem considerations
+
+- **`eslint-plugin-ember`** — A new lint rule (or an update to an existing rule) should be introduced to flag `this.set(…)` and `this.get(…)` calls inside `module(…)` / `test(…)` callbacks, guiding users toward the modern pattern.
+- **Blueprints** — Any existing blueprints in `ember-source` or `ember-cli` that generate rendering-test boilerplate using `this.set`/`this.get` should be updated to use the component-based pattern.
+- **Codemods** — A codemod (e.g. as part of `ember-codemods` or a standalone package) should be provided to automate the majority of the migration. Cases where the test drives complex state that touches multiple `this.set` calls will require manual attention, but simple single-value cases should be fully automatable.
+
+## How We Teach This
+
+The [Testing Components](https://guides.emberjs.com/release/testing/testing-components/) section of the official guides should be updated to:
+
+1. Remove all examples that use `this.set` / `this.get`.
+2. Present the `render(component)` + `rerender()` pattern as the canonical approach.
+3. Include a brief migration note linking to the deprecation guide on `deprecations.emberjs.com`.
+
+The API docs for `@ember/test-helpers` should likewise be updated to mark `TestContext#set` and `TestContext#get` as deprecated and point to the alternatives.
+
+A deprecation guide entry should be added to `deprecations.emberjs.com` covering:
+
+- What was deprecated and why.
+- The before/after code examples above.
+- Guidance for the less common edge cases (e.g. deeply nested `this.set` calls, helper-heavy templates).
+
+## Drawbacks
+
+- **Migration cost.** `this.set` and `this.get` have been in use since the beginning of Ember's testing story. Large codebases may have hundreds or thousands of test files that need updating. A well-maintained codemod should substantially reduce the burden.
+- **Loss of a simple entry point.** For simple tests, `this.set('value', x)` is arguably terser than introducing a tracked class. This cost is outweighed by the correctness and TypeScript benefits, but should be acknowledged in migration documentation.
+
+## Alternatives
+
+- **Do nothing.** Leave `this.set` / `this.get` available indefinitely. This leaves the inconsistency and TypeScript friction in place and means RFC #785's goal of a cleaner test model is never fully realized.
+- **Hard removal without a deprecation period.** Would be a breaking change and is not appropriate given how widespread the pattern is.
+
+## Unresolved questions
+
+- What is the appropriate Ember version for the deprecation to land in, and what is the target removal version (i.e. the next major)?
+- Should the deprecation be opt-in (gated by a flag in `@ember/test-helpers` config) initially, to allow teams to migrate on their own schedule, before becoming unconditional?
+- Should `this.owner` and other non-`get`/`set` test-context properties remain unaffected? (Yes — this RFC is scoped only to `get` and `set`.)