test(core): add type tests for ɵunwrapWritableSignal (#54387)

Getting the typing for `ɵunwrapWritableSignal` just right was tricky so these changes add some tests to ensure that we don't regress.

Also reworks the type tester a bit to make it easier to find where to add new test files.

PR Close #54387

packages/core/test/authoring/BUILD.bazel

@@ -7,6 +7,7 @@ ts_library(
         "signal_input_signature_test.ts",
         "signal_model_signature_test.ts",
         "signal_queries_signature_test.ts",
+        "unwrap_writable_signal_signature_test.ts",
     ],
     deps = ["//packages/core"],
 )

packages/core/test/authoring/type_tester.ts

@@ -11,6 +11,17 @@ import path from 'path';
 import ts from 'typescript';
 import url from 'url';
 
+/** Currently-configured tests. */
+const TESTS = new Map<string, (value: string) => string>([
+  [
+    'signal_input_signature_test',
+    v => v.includes(',') ? `InputSignalWithTransform<${v}>` : `InputSignal<${v}>`
+  ],
+  ['signal_queries_signature_test', v => `Signal<${v}>`],
+  ['signal_model_signature_test', v => `ModelSignal<${v}>`],
+  ['unwrap_writable_signal_signature_test', v => v]
+]);
+
 const containingDir = path.dirname(url.fileURLToPath(import.meta.url));
 
 /**
@@ -21,8 +32,7 @@ function isTestClass(classDeclaration: ts.ClassDeclaration): boolean {
   return classDeclaration.name !== undefined && classDeclaration.name.text.endsWith('Test');
 }
 
-function testFile(
-    testFileName: string, getType: (v: string) => string, inferWriteType: boolean): boolean {
+function testFile(testFileName: string, getType: (v: string) => string): boolean {
   const fileContent = fs.readFileSync(path.join(containingDir, `${testFileName}.d.ts`), 'utf8');
   const sourceFile = ts.createSourceFile('test.ts', fileContent, ts.ScriptTarget.ESNext, true);
   const testClazz = sourceFile.statements.find(
@@ -63,11 +73,7 @@ function testFile(
 async function main() {
   let failing = false;
 
-  failing ||= testFile(
-      'signal_input_signature_test',
-      v => v.includes(',') ? `InputSignalWithTransform<${v}>` : `InputSignal<${v}>`, true);
-  failing ||= testFile('signal_queries_signature_test', v => `Signal<${v}>`, false);
-  failing ||= testFile('signal_model_signature_test', v => `ModelSignal<${v}>`, false);
+  TESTS.forEach((callback, filename) => failing ||= testFile(filename, callback));
 
   if (failing) {
     throw new Error('Failing assertions');

packages/core/test/authoring/unwrap_writable_signal_signature_test.ts

@@ -0,0 +1,44 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+/**
+ * @fileoverview
+ * This file contains various signal `model()` patterns and ensures
+ * the resulting types match our expectations (via comments asserting the `.d.ts`).
+ */
+
+import {input, model, signal, ɵunwrapWritableSignal as unwrapWritableSignal} from '@angular/core';
+// clang-format off
+// import preserved to simplify `.d.ts` emit and simplify the `type_tester` logic.
+// tslint:disable-next-line no-duplicate-imports
+import {InputSignal, WritableSignal} from '@angular/core';
+// clang-format on
+
+export class SignalModelSignatureTest {
+  /** string | undefined */
+  optionalModel = unwrapWritableSignal(model<string>());
+
+  /** string */
+  requiredModel = unwrapWritableSignal(model.required<string>());
+
+  /** string | number */
+  writableSignal = unwrapWritableSignal(signal<string|number>(0));
+
+  /** InputSignal<string | undefined> */
+  optionalReadonlySignal = unwrapWritableSignal(input<string>());
+
+  /** InputSignal<string> */
+  requiredReadonlySignal = unwrapWritableSignal(input.required<string>());
+
+  /** number */
+  primitiveValue = unwrapWritableSignal(123);
+
+  /** (value: string | null | undefined) => number */
+  getterFunction =
+      unwrapWritableSignal((value: string|null|undefined) => value ? parseInt(value) : 0);
+}