feat(core-eslint): component-must-have-test rule

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/core-eslint/rules/component-must-have-test.test.js

@@ -0,0 +1,49 @@
+import { describe, it } from "vitest";
+import { RuleTester } from "eslint";
+import path from "node:path";
+import os from "node:os";
+import fs from "node:fs";
+import rule from "./component-must-have-test.js";
+
+function makeFixture({ withTest }) {
+  const root = fs.mkdtempSync(path.join(os.tmpdir(), "cmht-"));
+  const dir = path.join(root, "packages", "core-ui", "src", "atoms", "Button");
+  fs.mkdirSync(dir, { recursive: true });
+  const component = path.join(dir, "Button.tsx");
+  fs.writeFileSync(component, `export const Button = () => <button>x</button>;`);
+  if (withTest) {
+    fs.writeFileSync(path.join(dir, "Button.test.tsx"), `import { it } from "vitest"; it("works", () => {});`);
+  }
+  return { component };
+}
+
+const tester = new RuleTester({
+  languageOptions: {
+    parser: await import("@typescript-eslint/parser"),
+    ecmaVersion: "latest",
+    sourceType: "module",
+    parserOptions: { ecmaFeatures: { jsx: true } },
+  },
+});
+
+describe("component-must-have-test", () => {
+  it("passes when sibling .test.tsx exists", () => {
+    const { component } = makeFixture({ withTest: true });
+    tester.run("component-must-have-test", rule, {
+      valid: [{ filename: component, code: fs.readFileSync(component, "utf8") }],
+      invalid: [],
+    });
+  });
+
+  it("fires when no sibling .test.tsx exists", () => {
+    const { component } = makeFixture({ withTest: false });
+    tester.run("component-must-have-test", rule, {
+      valid: [],
+      invalid: [{
+        filename: component,
+        code: fs.readFileSync(component, "utf8"),
+        errors: [{ messageId: "missingTest" }],
+      }],
+    });
+  });
+});