feat: add util to check whether type is valid GitHub alert type

src/is-github-alert-type.test.ts

@@ -0,0 +1,29 @@
+import { describe, expect, it } from "vitest";
+import {isGithubAlertType} from "./is-github-alert-type.js";
+import {GithubAlertType} from "./github-alert.type.js";
+
+describe('is-github-alert-type', () => {
+  it('should return false for an undefined value', () => {
+    expect(isGithubAlertType(undefined)).toEqual(false);
+  });
+
+  it('should return false for a null value', () => {
+    expect(isGithubAlertType(null)).toEqual(false);
+  });
+
+  it('should return false for a string value not equal to a GitHub alert type', () => {
+    expect(isGithubAlertType("test")).toEqual(false);
+  });
+
+  it('should return true for a value directly taken from the GitHub alert type enum', () => {
+    expect(isGithubAlertType(GithubAlertType.WARNING)).toEqual(true);
+  });
+
+  it('should return true for a string value that equals an alert type', () => {
+    expect(isGithubAlertType("IMPORTANT")).toEqual(true);
+  });
+
+  it('should return false for a string value with the wrong capitalization', () => {
+    expect(isGithubAlertType("important")).toEqual(false);
+  });
+})

src/is-github-alert-type.ts

@@ -0,0 +1,5 @@
+import {GITHUB_ALERT_TYPES, type GithubAlertType} from "./github-alert.type.js";
+
+export function isGithubAlertType(type: unknown): type is GithubAlertType {
+  return GITHUB_ALERT_TYPES.includes(type as GithubAlertType);
+}