diff --git a/CHANGELOG.md b/CHANGELOG.md
index 94f98a0..5ce07fb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,7 @@ always bump at least minor; breaking schema changes bump major.
 - Add `infra/gitlab-ci` to the closed skill taxonomy (#24).
 
 ### Fixed
+- Go (`foo_test.go`), Python (`test_foo.py`) and Ruby (`foo_spec.rb`) test files are now categorised as `testing` instead of falling through to `backend`.
 - Improve manifest dependency detection by comparing parent and child
   revision snapshots instead of relying only on added diff lines. This now
   correctly detects dependencies added inside existing blocks in
diff --git a/src/categorize.ts b/src/categorize.ts
index fba1801..c5a1f45 100644
--- a/src/categorize.ts
+++ b/src/categorize.ts
@@ -8,7 +8,15 @@ import type { CategoryName } from "./types.js";
 //
 // Order matters: first matching rule wins.
 const RULES: Array<[RegExp, CategoryName]> = [
-  [/(^|\/)(__tests__|tests?|specs?)(\/|$)|\.(test|spec)\.[jt]sx?$/i, "testing"],
+  // Recognise test files across languages: a `test/` or `spec/` directory, the
+  // JS/TS `.test.`/`.spec.` infix, the `_test.`/`_spec.` suffix used by Go
+  // (`foo_test.go`), Ruby (`foo_spec.rb`) and others, and the Python `test_`
+  // prefix (`test_foo.py`). Previously only the JS/TS forms were matched, so
+  // `foo_test.go` and `test_foo.py` fell through to "backend".
+  [
+    /(^|\/)(__tests__|tests?|specs?)(\/|$)|[._](test|spec)\.[a-z0-9]+$|(^|\/)test_[^/]+\.[a-z0-9]+$/i,
+    "testing",
+  ],
   [/(^|\/)(claude\.md|agents\.md|\.cursor|\.aider|copilot)/i, "ai-workflow"],
   [
     /(^|\/)(\.github\/workflows|dockerfile|docker-compose|terraform|k8s|kubernetes|infra)(\/|$|\.)/i,
diff --git a/test/categorize.test.ts b/test/categorize.test.ts
new file mode 100644
index 0000000..5b11462
--- /dev/null
+++ b/test/categorize.test.ts
@@ -0,0 +1,22 @@
+import { describe, expect, it } from "vitest";
+
+import { categorize } from "../src/categorize.js";
+
+describe("categorize", () => {
+  it("classifies JS/TS test files as testing", () => {
+    expect(categorize("src/Button.test.tsx")).toBe("testing");
+    expect(categorize("__tests__/foo.ts")).toBe("testing");
+  });
+
+  it("classifies Go, Python and Ruby test files as testing", () => {
+    expect(categorize("pkg/foo_test.go")).toBe("testing");
+    expect(categorize("app/test_user.py")).toBe("testing");
+    expect(categorize("lib/user_spec.rb")).toBe("testing");
+  });
+
+  it("does not misclassify non-test source files", () => {
+    expect(categorize("src/api/users.go")).toBe("backend");
+    expect(categorize("src/latest.go")).toBe("backend");
+    expect(categorize("src/contest.py")).toBe("backend");
+  });
+});