From 041827dc5405e154a36b5e0ba8b46d21913344bf Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 5 Feb 2026 16:25:33 +0000
Subject: [PATCH 1/7] Initial plan


From cb97df58c929c562ab57d92fc0cd0ed4bf1086d1 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 5 Feb 2026 16:40:10 +0000
Subject: [PATCH 2/7] Migrate init templates to new testing framework

Co-authored-by: timotheeguerin <1031227+timotheeguerin@users.noreply.github.com>
---
 .../emitter-ts/test/hello.test.ts             |  2 +-
 .../emitter-ts/test/test-host.ts              | 43 +++++--------------
 .../library-ts/test/decorators.test.ts        | 33 ++++++--------
 .../library-ts/test/test-host.ts              | 24 ++++-------
 .../templates/emitter-ts/test/hello.test.ts   |  2 +-
 .../templates/emitter-ts/test/test-host.ts.mu | 43 +++++--------------
 .../library-ts/test/decorators.test.ts.mu     | 33 ++++++--------
 .../templates/library-ts/test/test-host.ts.mu | 24 ++++-------
 8 files changed, 62 insertions(+), 142 deletions(-)

diff --git a/packages/compiler/templates/__snapshots__/emitter-ts/test/hello.test.ts b/packages/compiler/templates/__snapshots__/emitter-ts/test/hello.test.ts
index 9bf04d106c1..00d8f062a17 100644
--- a/packages/compiler/templates/__snapshots__/emitter-ts/test/hello.test.ts
+++ b/packages/compiler/templates/__snapshots__/emitter-ts/test/hello.test.ts
@@ -1,5 +1,5 @@
 import { strictEqual } from "node:assert";
-import { describe, it } from "node:test";
+import { describe, it } from "vitest";
 import { emit } from "./test-host.js";
 
 describe("hello", () => {
diff --git a/packages/compiler/templates/__snapshots__/emitter-ts/test/test-host.ts b/packages/compiler/templates/__snapshots__/emitter-ts/test/test-host.ts
index 14b78cf71f5..2a0d323e463 100644
--- a/packages/compiler/templates/__snapshots__/emitter-ts/test/test-host.ts
+++ b/packages/compiler/templates/__snapshots__/emitter-ts/test/test-host.ts
@@ -1,43 +1,20 @@
 import { Diagnostic, resolvePath } from "@typespec/compiler";
-import {
-  createTestHost,
-  createTestWrapper,
-  expectDiagnosticEmpty,
-} from "@typespec/compiler/testing";
-import { EmitterTsTestLibrary } from "../src/testing/index.js";
+import { expectDiagnosticEmpty } from "@typespec/compiler/testing";
+import { createTester } from "@typespec/compiler/testing";
 
-export async function createEmitterTsTestHost() {
-  return createTestHost({
-    libraries: [EmitterTsTestLibrary],
-  });
-}
-
-export async function createEmitterTsTestRunner() {
-  const host = await createEmitterTsTestHost();
-
-  return createTestWrapper(host, {
-    compilerOptions: {
-      noEmit: false,
-      emit: ["emitter-ts"],
-    },
-  });
-}
+export const Tester = createTester(resolvePath(import.meta.dirname, ".."), {
+  libraries: ["emitter-ts"],
+}).emit("emitter-ts");
 
 export async function emitWithDiagnostics(
   code: string
 ): Promise<[Record<string, string>, readonly Diagnostic[]]> {
-  const runner = await createEmitterTsTestRunner();
-  await runner.compileAndDiagnose(code, {
-    outputDir: "tsp-output",
+  const [{ outputs }, diagnostics] = await Tester.compileAndDiagnose(code, {
+    compilerOptions: {
+      emit: ["emitter-ts"],
+    },
   });
-  const emitterOutputDir = "./tsp-output/emitter-ts";
-  const files = await runner.program.host.readDir(emitterOutputDir);
-
-  const result: Record<string, string> = {};
-  for (const file of files) {
-    result[file] = (await runner.program.host.readFile(resolvePath(emitterOutputDir, file))).text;
-  }
-  return [result, runner.program.diagnostics];
+  return [outputs, diagnostics];
 }
 
 export async function emit(code: string): Promise<Record<string, string>> {
diff --git a/packages/compiler/templates/__snapshots__/library-ts/test/decorators.test.ts b/packages/compiler/templates/__snapshots__/library-ts/test/decorators.test.ts
index b089e56bcd8..ab7e95e2f43 100644
--- a/packages/compiler/templates/__snapshots__/library-ts/test/decorators.test.ts
+++ b/packages/compiler/templates/__snapshots__/library-ts/test/decorators.test.ts
@@ -1,29 +1,22 @@
 import { strictEqual } from "node:assert";
-import { describe, it, beforeEach } from "node:test";
-import type { Operation } from "@typespec/compiler";
-import { BasicTestRunner, expectDiagnostics, extractCursor } from "@typespec/compiler/testing";
+import { describe, it } from "vitest";
+import { expectDiagnostics, extractCursor, t } from "@typespec/compiler/testing";
 import { getAlternateName } from "../src/decorators.js";
-import { createLibraryTsTestRunner } from "./test-host.js";
+import { Tester } from "./test-host.js";
 
 describe("decorators", () => {
-  let runner: BasicTestRunner;
-
-  beforeEach(async () => {
-    runner = await createLibraryTsTestRunner();
-  })
-
   describe("@alternateName", () => {
     it("set alternate name on operation", async () => {
-      const { test } = (await runner.compile(
-        `@alternateName("bar") @test op test(): void;`
-      )) as { test: Operation };
-      strictEqual(getAlternateName(runner.program, test), "bar");
+      const { test, program } = await Tester.compile(t.code`
+        @alternateName("bar") ${t.op("test")}(): void;
+      `);
+      strictEqual(getAlternateName(program, test), "bar");
     });
 
     it("emit diagnostic if not used on an operation", async () => {
-      const diagnostics = await runner.diagnose(
-        `@alternateName("bar") model Test {}`
-      );
+      const diagnostics = await Tester.diagnose(`
+        @alternateName("bar") model Test {}
+      `);
       expectDiagnostics(diagnostics, {
         severity: "error",
         code: "decorator-wrong-target",
@@ -34,14 +27,12 @@ describe("decorators", () => {
 
     it("emit diagnostic if using banned name", async () => {
       const {pos, source} = extractCursor(`@alternateName(┆"banned") op test(): void;`)
-      const diagnostics = await runner.diagnose(
-        source
-      );
+      const diagnostics = await Tester.diagnose(source);
       expectDiagnostics(diagnostics, {
         severity: "error",
         code: "library-ts/banned-alternate-name",
         message: `Banned alternate name "banned".`,
-        pos: pos + runner.autoCodeOffset
+        pos
       })
     });
   });
diff --git a/packages/compiler/templates/__snapshots__/library-ts/test/test-host.ts b/packages/compiler/templates/__snapshots__/library-ts/test/test-host.ts
index e973984e84b..852a8afc8b9 100644
--- a/packages/compiler/templates/__snapshots__/library-ts/test/test-host.ts
+++ b/packages/compiler/templates/__snapshots__/library-ts/test/test-host.ts
@@ -1,17 +1,9 @@
-import { createTestHost, createTestWrapper } from "@typespec/compiler/testing";
-import { LibraryTsTestLibrary } from "../src/testing/index.js";
-
-export async function createLibraryTsTestHost() {
-  return createTestHost({
-    libraries: [LibraryTsTestLibrary],
-  });
-}
-
-export async function createLibraryTsTestRunner() {
-  const host = await createLibraryTsTestHost();
-
-  return createTestWrapper(host, {
-    autoUsings: ["LibraryTs"]
-  });
-}
+import { resolvePath } from "@typespec/compiler";
+import { createTester } from "@typespec/compiler/testing";
+
+export const Tester = createTester(resolvePath(import.meta.dirname, ".."), {
+  libraries: ["library-ts"],
+})
+  .import("library-ts")
+  .using("LibraryTs");
 
diff --git a/packages/compiler/templates/emitter-ts/test/hello.test.ts b/packages/compiler/templates/emitter-ts/test/hello.test.ts
index 9bf04d106c1..00d8f062a17 100644
--- a/packages/compiler/templates/emitter-ts/test/hello.test.ts
+++ b/packages/compiler/templates/emitter-ts/test/hello.test.ts
@@ -1,5 +1,5 @@
 import { strictEqual } from "node:assert";
-import { describe, it } from "node:test";
+import { describe, it } from "vitest";
 import { emit } from "./test-host.js";
 
 describe("hello", () => {
diff --git a/packages/compiler/templates/emitter-ts/test/test-host.ts.mu b/packages/compiler/templates/emitter-ts/test/test-host.ts.mu
index 5f1f869861a..70d6b7fb7a2 100644
--- a/packages/compiler/templates/emitter-ts/test/test-host.ts.mu
+++ b/packages/compiler/templates/emitter-ts/test/test-host.ts.mu
@@ -1,43 +1,20 @@
 import { Diagnostic, resolvePath } from "@typespec/compiler";
-import {
-  createTestHost,
-  createTestWrapper,
-  expectDiagnosticEmpty,
-} from "@typespec/compiler/testing";
-import { {{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}TestLibrary } from "../src/testing/index.js";
+import { expectDiagnosticEmpty } from "@typespec/compiler/testing";
+import { createTester } from "@typespec/compiler/testing";
 
-export async function create{{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}TestHost() {
-  return createTestHost({
-    libraries: [{{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}TestLibrary],
-  });
-}
-
-export async function create{{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}TestRunner() {
-  const host = await create{{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}TestHost();
-
-  return createTestWrapper(host, {
-    compilerOptions: {
-      noEmit: false,
-      emit: ["{{name}}"],
-    },
-  });
-}
+export const Tester = createTester(resolvePath(import.meta.dirname, ".."), {
+  libraries: ["{{name}}"],
+}).emit("{{name}}");
 
 export async function emitWithDiagnostics(
   code: string
 ): Promise<[Record<string, string>, readonly Diagnostic[]]> {
-  const runner = await create{{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}TestRunner();
-  await runner.compileAndDiagnose(code, {
-    outputDir: "tsp-output",
+  const [{ outputs }, diagnostics] = await Tester.compileAndDiagnose(code, {
+    compilerOptions: {
+      emit: ["{{name}}"],
+    },
   });
-  const emitterOutputDir = "./tsp-output/{{name}}";
-  const files = await runner.program.host.readDir(emitterOutputDir);
-
-  const result: Record<string, string> = {};
-  for (const file of files) {
-    result[file] = (await runner.program.host.readFile(resolvePath(emitterOutputDir, file))).text;
-  }
-  return [result, runner.program.diagnostics];
+  return [outputs, diagnostics];
 }
 
 export async function emit(code: string): Promise<Record<string, string>> {
diff --git a/packages/compiler/templates/library-ts/test/decorators.test.ts.mu b/packages/compiler/templates/library-ts/test/decorators.test.ts.mu
index 18b154793df..5c87f21401a 100644
--- a/packages/compiler/templates/library-ts/test/decorators.test.ts.mu
+++ b/packages/compiler/templates/library-ts/test/decorators.test.ts.mu
@@ -1,29 +1,22 @@
 import { strictEqual } from "node:assert";
-import { describe, it, beforeEach } from "node:test";
-import type { Operation } from "@typespec/compiler";
-import { BasicTestRunner, expectDiagnostics, extractCursor } from "@typespec/compiler/testing";
+import { describe, it } from "vitest";
+import { expectDiagnostics, extractCursor, t } from "@typespec/compiler/testing";
 import { getAlternateName } from "../src/decorators.js";
-import { create{{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}TestRunner } from "./test-host.js";
+import { Tester } from "./test-host.js";
 
 describe("decorators", () => {
-  let runner: BasicTestRunner;
-
-  beforeEach(async () => {
-    runner = await create{{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}TestRunner();
-  })
-
   describe("@alternateName", () => {
     it("set alternate name on operation", async () => {
-      const { test } = (await runner.compile(
-        `@alternateName("bar") @test op test(): void;`
-      )) as { test: Operation };
-      strictEqual(getAlternateName(runner.program, test), "bar");
+      const { test, program } = await Tester.compile(t.code`
+        @alternateName("bar") ${t.op("test")}(): void;
+      `);
+      strictEqual(getAlternateName(program, test), "bar");
     });
 
     it("emit diagnostic if not used on an operation", async () => {
-      const diagnostics = await runner.diagnose(
-        `@alternateName("bar") model Test {}`
-      );
+      const diagnostics = await Tester.diagnose(`
+        @alternateName("bar") model Test {}
+      `);
       expectDiagnostics(diagnostics, {
         severity: "error",
         code: "decorator-wrong-target",
@@ -34,14 +27,12 @@ describe("decorators", () => {
 
     it("emit diagnostic if using banned name", async () => {
       const {pos, source} = extractCursor(`@alternateName(┆"banned") op test(): void;`)
-      const diagnostics = await runner.diagnose(
-        source
-      );
+      const diagnostics = await Tester.diagnose(source);
       expectDiagnostics(diagnostics, {
         severity: "error",
         code: "{{name}}/banned-alternate-name",
         message: `Banned alternate name "banned".`,
-        pos: pos + runner.autoCodeOffset
+        pos
       })
     });
   });
diff --git a/packages/compiler/templates/library-ts/test/test-host.ts.mu b/packages/compiler/templates/library-ts/test/test-host.ts.mu
index b75e5c1045d..a4b5aed5e7a 100644
--- a/packages/compiler/templates/library-ts/test/test-host.ts.mu
+++ b/packages/compiler/templates/library-ts/test/test-host.ts.mu
@@ -1,17 +1,9 @@
-import { createTestHost, createTestWrapper } from "@typespec/compiler/testing";
-import { {{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}TestLibrary } from "../src/testing/index.js";
-
-export async function create{{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}TestHost() {
-  return createTestHost({
-    libraries: [{{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}TestLibrary],
-  });
-}
-
-export async function create{{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}TestRunner() {
-  const host = await create{{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}TestHost();
-
-  return createTestWrapper(host, {
-    autoUsings: ["{{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}"]
-  });
-}
+import { resolvePath } from "@typespec/compiler";
+import { createTester } from "@typespec/compiler/testing";
+
+export const Tester = createTester(resolvePath(import.meta.dirname, ".."), {
+  libraries: ["{{name}}"],
+})
+  .import("{{name}}")
+  .using("{{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}");
 

From bc903f97def35a999f15ae1ba33539c863a2668b Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 5 Feb 2026 19:31:27 +0000
Subject: [PATCH 3/7] Revert vitest imports to node:test and fix tester path
 resolution

Co-authored-by: timotheeguerin <1031227+timotheeguerin@users.noreply.github.com>
---
 .../templates/__snapshots__/emitter-ts/test/hello.test.ts | 2 +-
 .../templates/__snapshots__/emitter-ts/test/test-host.ts  | 8 ++------
 .../__snapshots__/library-ts/test/decorators.test.ts      | 2 +-
 .../templates/__snapshots__/library-ts/test/test-host.ts  | 2 +-
 packages/compiler/templates/emitter-ts/test/hello.test.ts | 2 +-
 .../compiler/templates/emitter-ts/test/test-host.ts.mu    | 8 ++------
 .../templates/library-ts/test/decorators.test.ts.mu       | 2 +-
 .../compiler/templates/library-ts/test/test-host.ts.mu    | 2 +-
 8 files changed, 10 insertions(+), 18 deletions(-)

diff --git a/packages/compiler/templates/__snapshots__/emitter-ts/test/hello.test.ts b/packages/compiler/templates/__snapshots__/emitter-ts/test/hello.test.ts
index 00d8f062a17..9bf04d106c1 100644
--- a/packages/compiler/templates/__snapshots__/emitter-ts/test/hello.test.ts
+++ b/packages/compiler/templates/__snapshots__/emitter-ts/test/hello.test.ts
@@ -1,5 +1,5 @@
 import { strictEqual } from "node:assert";
-import { describe, it } from "vitest";
+import { describe, it } from "node:test";
 import { emit } from "./test-host.js";
 
 describe("hello", () => {
diff --git a/packages/compiler/templates/__snapshots__/emitter-ts/test/test-host.ts b/packages/compiler/templates/__snapshots__/emitter-ts/test/test-host.ts
index 2a0d323e463..8e62dac4d01 100644
--- a/packages/compiler/templates/__snapshots__/emitter-ts/test/test-host.ts
+++ b/packages/compiler/templates/__snapshots__/emitter-ts/test/test-host.ts
@@ -2,18 +2,14 @@ import { Diagnostic, resolvePath } from "@typespec/compiler";
 import { expectDiagnosticEmpty } from "@typespec/compiler/testing";
 import { createTester } from "@typespec/compiler/testing";
 
-export const Tester = createTester(resolvePath(import.meta.dirname, ".."), {
+export const Tester = createTester(resolvePath(import.meta.dirname, "../.."), {
   libraries: ["emitter-ts"],
 }).emit("emitter-ts");
 
 export async function emitWithDiagnostics(
   code: string
 ): Promise<[Record<string, string>, readonly Diagnostic[]]> {
-  const [{ outputs }, diagnostics] = await Tester.compileAndDiagnose(code, {
-    compilerOptions: {
-      emit: ["emitter-ts"],
-    },
-  });
+  const [{ outputs }, diagnostics] = await Tester.compileAndDiagnose(code);
   return [outputs, diagnostics];
 }
 
diff --git a/packages/compiler/templates/__snapshots__/library-ts/test/decorators.test.ts b/packages/compiler/templates/__snapshots__/library-ts/test/decorators.test.ts
index ab7e95e2f43..332167df685 100644
--- a/packages/compiler/templates/__snapshots__/library-ts/test/decorators.test.ts
+++ b/packages/compiler/templates/__snapshots__/library-ts/test/decorators.test.ts
@@ -1,5 +1,5 @@
 import { strictEqual } from "node:assert";
-import { describe, it } from "vitest";
+import { describe, it } from "node:test";
 import { expectDiagnostics, extractCursor, t } from "@typespec/compiler/testing";
 import { getAlternateName } from "../src/decorators.js";
 import { Tester } from "./test-host.js";
diff --git a/packages/compiler/templates/__snapshots__/library-ts/test/test-host.ts b/packages/compiler/templates/__snapshots__/library-ts/test/test-host.ts
index 852a8afc8b9..75009f5369e 100644
--- a/packages/compiler/templates/__snapshots__/library-ts/test/test-host.ts
+++ b/packages/compiler/templates/__snapshots__/library-ts/test/test-host.ts
@@ -1,7 +1,7 @@
 import { resolvePath } from "@typespec/compiler";
 import { createTester } from "@typespec/compiler/testing";
 
-export const Tester = createTester(resolvePath(import.meta.dirname, ".."), {
+export const Tester = createTester(resolvePath(import.meta.dirname, "../.."), {
   libraries: ["library-ts"],
 })
   .import("library-ts")
diff --git a/packages/compiler/templates/emitter-ts/test/hello.test.ts b/packages/compiler/templates/emitter-ts/test/hello.test.ts
index 00d8f062a17..9bf04d106c1 100644
--- a/packages/compiler/templates/emitter-ts/test/hello.test.ts
+++ b/packages/compiler/templates/emitter-ts/test/hello.test.ts
@@ -1,5 +1,5 @@
 import { strictEqual } from "node:assert";
-import { describe, it } from "vitest";
+import { describe, it } from "node:test";
 import { emit } from "./test-host.js";
 
 describe("hello", () => {
diff --git a/packages/compiler/templates/emitter-ts/test/test-host.ts.mu b/packages/compiler/templates/emitter-ts/test/test-host.ts.mu
index 70d6b7fb7a2..950a699f0fa 100644
--- a/packages/compiler/templates/emitter-ts/test/test-host.ts.mu
+++ b/packages/compiler/templates/emitter-ts/test/test-host.ts.mu
@@ -2,18 +2,14 @@ import { Diagnostic, resolvePath } from "@typespec/compiler";
 import { expectDiagnosticEmpty } from "@typespec/compiler/testing";
 import { createTester } from "@typespec/compiler/testing";
 
-export const Tester = createTester(resolvePath(import.meta.dirname, ".."), {
+export const Tester = createTester(resolvePath(import.meta.dirname, "../.."), {
   libraries: ["{{name}}"],
 }).emit("{{name}}");
 
 export async function emitWithDiagnostics(
   code: string
 ): Promise<[Record<string, string>, readonly Diagnostic[]]> {
-  const [{ outputs }, diagnostics] = await Tester.compileAndDiagnose(code, {
-    compilerOptions: {
-      emit: ["{{name}}"],
-    },
-  });
+  const [{ outputs }, diagnostics] = await Tester.compileAndDiagnose(code);
   return [outputs, diagnostics];
 }
 
diff --git a/packages/compiler/templates/library-ts/test/decorators.test.ts.mu b/packages/compiler/templates/library-ts/test/decorators.test.ts.mu
index 5c87f21401a..48129fd9917 100644
--- a/packages/compiler/templates/library-ts/test/decorators.test.ts.mu
+++ b/packages/compiler/templates/library-ts/test/decorators.test.ts.mu
@@ -1,5 +1,5 @@
 import { strictEqual } from "node:assert";
-import { describe, it } from "vitest";
+import { describe, it } from "node:test";
 import { expectDiagnostics, extractCursor, t } from "@typespec/compiler/testing";
 import { getAlternateName } from "../src/decorators.js";
 import { Tester } from "./test-host.js";
diff --git a/packages/compiler/templates/library-ts/test/test-host.ts.mu b/packages/compiler/templates/library-ts/test/test-host.ts.mu
index a4b5aed5e7a..d9bb3fbf1b3 100644
--- a/packages/compiler/templates/library-ts/test/test-host.ts.mu
+++ b/packages/compiler/templates/library-ts/test/test-host.ts.mu
@@ -1,7 +1,7 @@
 import { resolvePath } from "@typespec/compiler";
 import { createTester } from "@typespec/compiler/testing";
 
-export const Tester = createTester(resolvePath(import.meta.dirname, ".."), {
+export const Tester = createTester(resolvePath(import.meta.dirname, "../.."), {
   libraries: ["{{name}}"],
 })
   .import("{{name}}")

From be7154b8fe2c7628bb726083fa7c75487a6b309f Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 5 Feb 2026 19:42:46 +0000
Subject: [PATCH 4/7] Update eslint config to latest standard with
 typescript-eslint package

Co-authored-by: timotheeguerin <1031227+timotheeguerin@users.noreply.github.com>
---
 .../templates/__snapshots__/emitter-ts/eslint.config.js   | 8 ++++++++
 .../templates/__snapshots__/emitter-ts/package.json       | 3 +--
 .../templates/__snapshots__/library-ts/eslint.config.js   | 8 ++++++++
 .../templates/__snapshots__/library-ts/package.json       | 3 +--
 packages/compiler/templates/emitter-ts/eslint.config.js   | 8 ++++++++
 packages/compiler/templates/emitter-ts/package.json       | 3 +--
 packages/compiler/templates/library-ts/eslint.config.js   | 8 ++++++++
 packages/compiler/templates/library-ts/package.json       | 3 +--
 8 files changed, 36 insertions(+), 8 deletions(-)

diff --git a/packages/compiler/templates/__snapshots__/emitter-ts/eslint.config.js b/packages/compiler/templates/__snapshots__/emitter-ts/eslint.config.js
index 75cb4f7ce3e..1bcb62d80de 100644
--- a/packages/compiler/templates/__snapshots__/emitter-ts/eslint.config.js
+++ b/packages/compiler/templates/__snapshots__/emitter-ts/eslint.config.js
@@ -8,4 +8,12 @@ export default tsEslint.config(
   },
   eslint.configs.recommended,
   ...tsEslint.configs.recommended,
+  {
+    rules: {
+      "@typescript-eslint/no-unused-vars": [
+        "warn",
+        { varsIgnorePattern: "^_", argsIgnorePattern: "^_" },
+      ],
+    },
+  },
 );
diff --git a/packages/compiler/templates/__snapshots__/emitter-ts/package.json b/packages/compiler/templates/__snapshots__/emitter-ts/package.json
index f9f12501c17..8231ab14f7b 100644
--- a/packages/compiler/templates/__snapshots__/emitter-ts/package.json
+++ b/packages/compiler/templates/__snapshots__/emitter-ts/package.json
@@ -18,8 +18,7 @@
   },
   "devDependencies": {
     "@types/node": "latest",
-    "@typescript-eslint/eslint-plugin": "^8.15.0",
-    "@typescript-eslint/parser": "^8.15.0",
+    "typescript-eslint": "^8.49.0",
     "eslint": "^9.15.0",
     "@typespec/compiler": "latest",
     "typescript": "^5.3.3",
diff --git a/packages/compiler/templates/__snapshots__/library-ts/eslint.config.js b/packages/compiler/templates/__snapshots__/library-ts/eslint.config.js
index 75cb4f7ce3e..1bcb62d80de 100644
--- a/packages/compiler/templates/__snapshots__/library-ts/eslint.config.js
+++ b/packages/compiler/templates/__snapshots__/library-ts/eslint.config.js
@@ -8,4 +8,12 @@ export default tsEslint.config(
   },
   eslint.configs.recommended,
   ...tsEslint.configs.recommended,
+  {
+    rules: {
+      "@typescript-eslint/no-unused-vars": [
+        "warn",
+        { varsIgnorePattern: "^_", argsIgnorePattern: "^_" },
+      ],
+    },
+  },
 );
diff --git a/packages/compiler/templates/__snapshots__/library-ts/package.json b/packages/compiler/templates/__snapshots__/library-ts/package.json
index 408d5aac9ae..5e2377b221b 100644
--- a/packages/compiler/templates/__snapshots__/library-ts/package.json
+++ b/packages/compiler/templates/__snapshots__/library-ts/package.json
@@ -19,8 +19,7 @@
   },
   "devDependencies": {
     "@types/node": "latest",
-    "@typescript-eslint/eslint-plugin": "^8.15.0",
-    "@typescript-eslint/parser": "^8.15.0",
+    "typescript-eslint": "^8.49.0",
     "@typespec/compiler": "latest",
     "@typespec/library-linter": "latest",
     "eslint": "^9.15.0",
diff --git a/packages/compiler/templates/emitter-ts/eslint.config.js b/packages/compiler/templates/emitter-ts/eslint.config.js
index 75cb4f7ce3e..1bcb62d80de 100644
--- a/packages/compiler/templates/emitter-ts/eslint.config.js
+++ b/packages/compiler/templates/emitter-ts/eslint.config.js
@@ -8,4 +8,12 @@ export default tsEslint.config(
   },
   eslint.configs.recommended,
   ...tsEslint.configs.recommended,
+  {
+    rules: {
+      "@typescript-eslint/no-unused-vars": [
+        "warn",
+        { varsIgnorePattern: "^_", argsIgnorePattern: "^_" },
+      ],
+    },
+  },
 );
diff --git a/packages/compiler/templates/emitter-ts/package.json b/packages/compiler/templates/emitter-ts/package.json
index 96ca29f0f73..1c9baaf7d2c 100644
--- a/packages/compiler/templates/emitter-ts/package.json
+++ b/packages/compiler/templates/emitter-ts/package.json
@@ -18,8 +18,7 @@
   },
   "devDependencies": {
     "@types/node": "latest",
-    "@typescript-eslint/eslint-plugin": "^8.15.0",
-    "@typescript-eslint/parser": "^8.15.0",
+    "typescript-eslint": "^8.49.0",
     "eslint": "^9.15.0",
     "@typespec/compiler": "latest",
     "typescript": "^5.3.3",
diff --git a/packages/compiler/templates/library-ts/eslint.config.js b/packages/compiler/templates/library-ts/eslint.config.js
index 75cb4f7ce3e..1bcb62d80de 100644
--- a/packages/compiler/templates/library-ts/eslint.config.js
+++ b/packages/compiler/templates/library-ts/eslint.config.js
@@ -8,4 +8,12 @@ export default tsEslint.config(
   },
   eslint.configs.recommended,
   ...tsEslint.configs.recommended,
+  {
+    rules: {
+      "@typescript-eslint/no-unused-vars": [
+        "warn",
+        { varsIgnorePattern: "^_", argsIgnorePattern: "^_" },
+      ],
+    },
+  },
 );
diff --git a/packages/compiler/templates/library-ts/package.json b/packages/compiler/templates/library-ts/package.json
index 2a104d5c60b..456e579ed0a 100644
--- a/packages/compiler/templates/library-ts/package.json
+++ b/packages/compiler/templates/library-ts/package.json
@@ -19,8 +19,7 @@
   },
   "devDependencies": {
     "@types/node": "latest",
-    "@typescript-eslint/eslint-plugin": "^8.15.0",
-    "@typescript-eslint/parser": "^8.15.0",
+    "typescript-eslint": "^8.49.0",
     "@typespec/compiler": "latest",
     "@typespec/library-linter": "latest",
     "eslint": "^9.15.0",

From 6f97eac0172a11784ee318e826d432fc188d56bf Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 5 Feb 2026 20:02:25 +0000
Subject: [PATCH 5/7] Replace tsEslint.config with defineConfig from
 eslint/config

Co-authored-by: timotheeguerin <1031227+timotheeguerin@users.noreply.github.com>
---
 .../templates/__snapshots__/emitter-ts/eslint.config.js        | 3 ++-
 .../templates/__snapshots__/library-ts/eslint.config.js        | 3 ++-
 packages/compiler/templates/emitter-ts/eslint.config.js        | 3 ++-
 packages/compiler/templates/library-ts/eslint.config.js        | 3 ++-
 4 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/packages/compiler/templates/__snapshots__/emitter-ts/eslint.config.js b/packages/compiler/templates/__snapshots__/emitter-ts/eslint.config.js
index 1bcb62d80de..430df9c59ea 100644
--- a/packages/compiler/templates/__snapshots__/emitter-ts/eslint.config.js
+++ b/packages/compiler/templates/__snapshots__/emitter-ts/eslint.config.js
@@ -1,8 +1,9 @@
 // @ts-check
 import eslint from "@eslint/js";
+import { defineConfig } from "eslint/config";
 import tsEslint from "typescript-eslint";
 
-export default tsEslint.config(
+export default defineConfig(
   {
     ignores: ["**/dist/**/*", "**/.temp/**/*"],
   },
diff --git a/packages/compiler/templates/__snapshots__/library-ts/eslint.config.js b/packages/compiler/templates/__snapshots__/library-ts/eslint.config.js
index 1bcb62d80de..430df9c59ea 100644
--- a/packages/compiler/templates/__snapshots__/library-ts/eslint.config.js
+++ b/packages/compiler/templates/__snapshots__/library-ts/eslint.config.js
@@ -1,8 +1,9 @@
 // @ts-check
 import eslint from "@eslint/js";
+import { defineConfig } from "eslint/config";
 import tsEslint from "typescript-eslint";
 
-export default tsEslint.config(
+export default defineConfig(
   {
     ignores: ["**/dist/**/*", "**/.temp/**/*"],
   },
diff --git a/packages/compiler/templates/emitter-ts/eslint.config.js b/packages/compiler/templates/emitter-ts/eslint.config.js
index 1bcb62d80de..430df9c59ea 100644
--- a/packages/compiler/templates/emitter-ts/eslint.config.js
+++ b/packages/compiler/templates/emitter-ts/eslint.config.js
@@ -1,8 +1,9 @@
 // @ts-check
 import eslint from "@eslint/js";
+import { defineConfig } from "eslint/config";
 import tsEslint from "typescript-eslint";
 
-export default tsEslint.config(
+export default defineConfig(
   {
     ignores: ["**/dist/**/*", "**/.temp/**/*"],
   },
diff --git a/packages/compiler/templates/library-ts/eslint.config.js b/packages/compiler/templates/library-ts/eslint.config.js
index 1bcb62d80de..430df9c59ea 100644
--- a/packages/compiler/templates/library-ts/eslint.config.js
+++ b/packages/compiler/templates/library-ts/eslint.config.js
@@ -1,8 +1,9 @@
 // @ts-check
 import eslint from "@eslint/js";
+import { defineConfig } from "eslint/config";
 import tsEslint from "typescript-eslint";
 
-export default tsEslint.config(
+export default defineConfig(
   {
     ignores: ["**/dist/**/*", "**/.temp/**/*"],
   },

From 46659d8baf7c829df7509bc506a2fd02f91db4d3 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 5 Feb 2026 20:12:12 +0000
Subject: [PATCH 6/7] Add changelog for init templates migration

Co-authored-by: timotheeguerin <1031227+timotheeguerin@users.noreply.github.com>
---
 ...e-init-templates-testing-framework-2026-1-5-20-11-37.md | 7 +++++++
 1 file changed, 7 insertions(+)
 create mode 100644 .chronus/changes/copilot-update-init-templates-testing-framework-2026-1-5-20-11-37.md

diff --git a/.chronus/changes/copilot-update-init-templates-testing-framework-2026-1-5-20-11-37.md b/.chronus/changes/copilot-update-init-templates-testing-framework-2026-1-5-20-11-37.md
new file mode 100644
index 00000000000..cf2f9c23e28
--- /dev/null
+++ b/.chronus/changes/copilot-update-init-templates-testing-framework-2026-1-5-20-11-37.md
@@ -0,0 +1,7 @@
+---
+changeKind: internal
+packages:
+  - "@typespec/compiler"
+---
+
+Update init templates to use createTester API and modern ESLint configuration
\ No newline at end of file

From 7ccf337c902f62f6ce9d816a57b67edc2769796b Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Fri, 6 Feb 2026 14:53:36 +0000
Subject: [PATCH 7/7] Fix library-ts template tests to work with createTester

Co-authored-by: timotheeguerin <1031227+timotheeguerin@users.noreply.github.com>
---
 .../library-ts/test/decorators.test.ts        | 20 +++++++++++--------
 .../library-ts/test/test-host.ts              |  4 +---
 .../library-ts/test/decorators.test.ts.mu     | 20 +++++++++++--------
 .../templates/library-ts/test/test-host.ts.mu |  4 +---
 4 files changed, 26 insertions(+), 22 deletions(-)

diff --git a/packages/compiler/templates/__snapshots__/library-ts/test/decorators.test.ts b/packages/compiler/templates/__snapshots__/library-ts/test/decorators.test.ts
index 332167df685..51ee4d92418 100644
--- a/packages/compiler/templates/__snapshots__/library-ts/test/decorators.test.ts
+++ b/packages/compiler/templates/__snapshots__/library-ts/test/decorators.test.ts
@@ -1,20 +1,23 @@
 import { strictEqual } from "node:assert";
 import { describe, it } from "node:test";
-import { expectDiagnostics, extractCursor, t } from "@typespec/compiler/testing";
+import type { Operation, Program } from "@typespec/compiler";
+import { expectDiagnostics } from "@typespec/compiler/testing";
 import { getAlternateName } from "../src/decorators.js";
 import { Tester } from "./test-host.js";
 
 describe("decorators", () => {
   describe("@alternateName", () => {
     it("set alternate name on operation", async () => {
-      const { test, program } = await Tester.compile(t.code`
-        @alternateName("bar") ${t.op("test")}(): void;
-      `);
+      const { test, program } = (await Tester.compile(`
+        using LibraryTs;
+        @alternateName("bar") @test op test(): void;
+      `)) as unknown as { test: Operation; program: Program };
       strictEqual(getAlternateName(program, test), "bar");
     });
 
     it("emit diagnostic if not used on an operation", async () => {
       const diagnostics = await Tester.diagnose(`
+        using LibraryTs;
         @alternateName("bar") model Test {}
       `);
       expectDiagnostics(diagnostics, {
@@ -26,13 +29,14 @@ describe("decorators", () => {
 
 
     it("emit diagnostic if using banned name", async () => {
-      const {pos, source} = extractCursor(`@alternateName(┆"banned") op test(): void;`)
-      const diagnostics = await Tester.diagnose(source);
+      const diagnostics = await Tester.diagnose(`
+        using LibraryTs;
+        @alternateName("banned") op test(): void;
+      `);
       expectDiagnostics(diagnostics, {
         severity: "error",
         code: "library-ts/banned-alternate-name",
-        message: `Banned alternate name "banned".`,
-        pos
+        message: `Banned alternate name "banned".`
       })
     });
   });
diff --git a/packages/compiler/templates/__snapshots__/library-ts/test/test-host.ts b/packages/compiler/templates/__snapshots__/library-ts/test/test-host.ts
index 75009f5369e..588a223c42b 100644
--- a/packages/compiler/templates/__snapshots__/library-ts/test/test-host.ts
+++ b/packages/compiler/templates/__snapshots__/library-ts/test/test-host.ts
@@ -3,7 +3,5 @@ import { createTester } from "@typespec/compiler/testing";
 
 export const Tester = createTester(resolvePath(import.meta.dirname, "../.."), {
   libraries: ["library-ts"],
-})
-  .import("library-ts")
-  .using("LibraryTs");
+}).import("library-ts");
 
diff --git a/packages/compiler/templates/library-ts/test/decorators.test.ts.mu b/packages/compiler/templates/library-ts/test/decorators.test.ts.mu
index 48129fd9917..f79480f86f2 100644
--- a/packages/compiler/templates/library-ts/test/decorators.test.ts.mu
+++ b/packages/compiler/templates/library-ts/test/decorators.test.ts.mu
@@ -1,20 +1,23 @@
 import { strictEqual } from "node:assert";
 import { describe, it } from "node:test";
-import { expectDiagnostics, extractCursor, t } from "@typespec/compiler/testing";
+import type { Operation, Program } from "@typespec/compiler";
+import { expectDiagnostics } from "@typespec/compiler/testing";
 import { getAlternateName } from "../src/decorators.js";
 import { Tester } from "./test-host.js";
 
 describe("decorators", () => {
   describe("@alternateName", () => {
     it("set alternate name on operation", async () => {
-      const { test, program } = await Tester.compile(t.code`
-        @alternateName("bar") ${t.op("test")}(): void;
-      `);
+      const { test, program } = (await Tester.compile(`
+        using {{#casing.pascalCase}}{{name}}{{/casing.pascalCase}};
+        @alternateName("bar") @test op test(): void;
+      `)) as unknown as { test: Operation; program: Program };
       strictEqual(getAlternateName(program, test), "bar");
     });
 
     it("emit diagnostic if not used on an operation", async () => {
       const diagnostics = await Tester.diagnose(`
+        using {{#casing.pascalCase}}{{name}}{{/casing.pascalCase}};
         @alternateName("bar") model Test {}
       `);
       expectDiagnostics(diagnostics, {
@@ -26,13 +29,14 @@ describe("decorators", () => {
 
 
     it("emit diagnostic if using banned name", async () => {
-      const {pos, source} = extractCursor(`@alternateName(┆"banned") op test(): void;`)
-      const diagnostics = await Tester.diagnose(source);
+      const diagnostics = await Tester.diagnose(`
+        using {{#casing.pascalCase}}{{name}}{{/casing.pascalCase}};
+        @alternateName("banned") op test(): void;
+      `);
       expectDiagnostics(diagnostics, {
         severity: "error",
         code: "{{name}}/banned-alternate-name",
-        message: `Banned alternate name "banned".`,
-        pos
+        message: `Banned alternate name "banned".`
       })
     });
   });
diff --git a/packages/compiler/templates/library-ts/test/test-host.ts.mu b/packages/compiler/templates/library-ts/test/test-host.ts.mu
index d9bb3fbf1b3..e87ec478d83 100644
--- a/packages/compiler/templates/library-ts/test/test-host.ts.mu
+++ b/packages/compiler/templates/library-ts/test/test-host.ts.mu
@@ -3,7 +3,5 @@ import { createTester } from "@typespec/compiler/testing";
 
 export const Tester = createTester(resolvePath(import.meta.dirname, "../.."), {
   libraries: ["{{name}}"],
-})
-  .import("{{name}}")
-  .using("{{#casing.pascalCase}}{{name}}{{/casing.pascalCase}}");
+}).import("{{name}}");