From f933ca74ff9df8b738d2089cfcbbb18ae50a9636 Mon Sep 17 00:00:00 2001
From: Danijel Martinek <danijel@fraqtal.xyz>
Date: Wed, 13 May 2026 07:40:40 +0200
Subject: [PATCH] feat(core-eslint): component-must-have-test rule

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 .../rules/component-must-have-test.js         | 53 +++++++++++++++++++
 .../rules/component-must-have-test.test.js    | 49 +++++++++++++++++
 2 files changed, 102 insertions(+)
 create mode 100644 packages/core-eslint/rules/component-must-have-test.js
 create mode 100644 packages/core-eslint/rules/component-must-have-test.test.js

diff --git a/packages/core-eslint/rules/component-must-have-test.js b/packages/core-eslint/rules/component-must-have-test.js
new file mode 100644
index 0000000..dd45df3
--- /dev/null
+++ b/packages/core-eslint/rules/component-must-have-test.js
@@ -0,0 +1,53 @@
+import fs from "node:fs";
+import path from "node:path";
+
+function isComponentFile(filename) {
+  if (!filename.endsWith(".tsx")) return false;
+  const base = path.basename(filename);
+  if (
+    base === "index.tsx" ||
+    base.endsWith(".test.tsx") ||
+    base.endsWith(".stories.tsx") ||
+    base.endsWith(".spec.tsx")
+  ) {
+    return false;
+  }
+  return (
+    filename.includes("/packages/core-ui/src/") ||
+    /\/packages\/[^/]+\/src\/ui\//.test(filename)
+  );
+}
+
+/** @type {import("eslint").Rule.RuleModule} */
+export default {
+  meta: {
+    type: "problem",
+    docs: {
+      description:
+        "Every component file must have a sibling *.test.tsx for behavioural coverage.",
+    },
+    schema: [],
+    messages: {
+      missingTest:
+        "Component {{filename}} has no sibling test at {{expected}}. Write the red test first.",
+    },
+  },
+  create(context) {
+    return {
+      Program(node) {
+        const filename = context.filename;
+        if (!isComponentFile(filename)) return;
+        const expected = filename.replace(/\.tsx$/, ".test.tsx");
+        if (fs.existsSync(expected)) return;
+        context.report({
+          node,
+          messageId: "missingTest",
+          data: {
+            filename: path.basename(filename),
+            expected: path.basename(expected),
+          },
+        });
+      },
+    };
+  },
+};
diff --git a/packages/core-eslint/rules/component-must-have-test.test.js b/packages/core-eslint/rules/component-must-have-test.test.js
new file mode 100644
index 0000000..398826c
--- /dev/null
+++ b/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" }],
+      }],
+    });
+  });
+});