test(dev-infra): extract commit message build function into testing util function (#41476)

Creates a testing utility function to build commit message strings.

PR Close #41476

dev-infra/commit-message/parse.spec.ts

@@ -7,9 +7,9 @@
  */
 
 import {parseCommitMessage} from './parse';
+import {commitMessageBuilder, CommitMessageParts} from './test-util';
 
-
+const commitValues: CommitMessageParts = {
-const commitValues = {
   prefix: '',
   type: 'fix',
   npmScope: '',
@@ -19,12 +19,7 @@ const commitValues = {
   footer: 'Closes #1',
 };
 
-function buildCommitMessage(params: Partial<typeof commitValues> = {}) {
+const buildCommitMessage = commitMessageBuilder(commitValues);
-  const {prefix, npmScope, type, scope, summary, body, footer} = {...commitValues, ...params};
-  const scopeSlug = npmScope ? `${npmScope}/${scope}` : scope;
-  return `${prefix}${type}${scopeSlug ? '(' + scopeSlug + ')' : ''}: ${summary}\n\n${body}\n\n${
-      footer}`;
-}
 
 
 describe('commit message parsing:', () => {

dev-infra/commit-message/test-util.ts

@@ -0,0 +1,30 @@
+/**
+ * @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
+ */
+
+/** The parts that make up a commit message for creating a commit message string. */
+export interface CommitMessageParts {
+  prefix: string;
+  type: string;
+  npmScope: string;
+  scope: string;
+  summary: string;
+  body: string;
+  footer: string;
+}
+
+/**
+ * Generate a commit message builder function, using the provided defaults.
+ */
+export function commitMessageBuilder(defaults: CommitMessageParts) {
+  return (params: Partial<CommitMessageParts> = {}) => {
+    const {prefix, type, npmScope, scope, summary, body, footer} = {...defaults, ...params};
+    const scopeSlug = npmScope ? `${npmScope}/${scope}` : scope;
+    return `${prefix}${type}${scopeSlug ? '(' + scopeSlug + ')' : ''}: ${summary}\n\n${body}\n\n${
+        footer}`;
+  };
+}