diff --git a/testing/backend/unit/test_validate_doc_links.py b/testing/backend/unit/test_validate_doc_links.py
new file mode 100644
index 000000000..ba322cf0d
--- /dev/null
+++ b/testing/backend/unit/test_validate_doc_links.py
@@ -0,0 +1,92 @@
+"""
+Unit tests for scripts/validate_doc_links.py
+
+Covers the three failure cases the documentation link validator must catch:
+  1. Relative links to files that exist (should pass, no error).
+  2. Links to missing files (should report a broken link).
+  3. Links with a #fragment whose heading anchor is missing (broken anchor).
+"""
+
+import importlib.util
+import pathlib
+
+import pytest
+
+
+# ── Load the script module by file path (it lives in scripts/, not a package) ──
+def _load_validator():
+    here = pathlib.Path(__file__).resolve()
+    for parent in here.parents:
+        candidate = parent / "scripts" / "validate_doc_links.py"
+        if candidate.exists():
+            spec = importlib.util.spec_from_file_location(
+                "validate_doc_links", candidate
+            )
+            module = importlib.util.module_from_spec(spec)
+            spec.loader.exec_module(module)
+            return module
+    raise FileNotFoundError("scripts/validate_doc_links.py not found")
+
+
+vdl = _load_validator()
+
+
+# ── slugify: pure function, quick sanity check ────────────────────────────────
+def test_slugify_matches_github_style():
+    assert vdl.slugify("Setup Guide") == "setup-guide"
+    assert vdl.slugify("Quick Start!") == "quick-start"
+
+
+# ── Case 1: a valid relative link + valid anchor → no errors ──────────────────
+def test_valid_relative_link_and_anchor(tmp_path, monkeypatch):
+    monkeypatch.setattr(vdl, "REPO_ROOT", tmp_path.resolve())
+
+    target = tmp_path / "guide.md"
+    target.write_text("# Setup Guide\n\nsome text\n", encoding="utf-8")
+
+    src = tmp_path / "README.md"
+    src.write_text("[guide](guide.md#setup-guide)\n", encoding="utf-8")
+
+    errors = vdl.validate_file(src)
+    assert errors == []
+
+
+# ── Case 2: link to a missing file → one "broken link target" error ───────────
+def test_missing_file_link_reported(tmp_path, monkeypatch):
+    monkeypatch.setattr(vdl, "REPO_ROOT", tmp_path.resolve())
+
+    src = tmp_path / "README.md"
+    src.write_text("[docs](docs/does_not_exist.md)\n", encoding="utf-8")
+
+    errors = vdl.validate_file(src)
+    assert len(errors) == 1
+    assert "broken link target" in errors[0]
+
+
+# ── Case 3: link with a broken #anchor → one "anchor ... not found" error ──────
+def test_broken_anchor_reported(tmp_path, monkeypatch):
+    monkeypatch.setattr(vdl, "REPO_ROOT", tmp_path.resolve())
+
+    target = tmp_path / "guide.md"
+    target.write_text("# Real Heading\n", encoding="utf-8")
+
+    src = tmp_path / "README.md"
+    src.write_text("[guide](guide.md#nonexistent-heading)\n", encoding="utf-8")
+
+    errors = vdl.validate_file(src)
+    assert len(errors) == 1
+    assert "anchor" in errors[0]
+
+
+# ── External URLs, in-page anchors, mailto links are skipped (no false errors) ─
+def test_external_and_inpage_links_skipped(tmp_path, monkeypatch):
+    monkeypatch.setattr(vdl, "REPO_ROOT", tmp_path.resolve())
+
+    src = tmp_path / "README.md"
+    src.write_text(
+        "[web](https://example.com) [top](#intro) [mail](mailto:a@b.com)\n",
+        encoding="utf-8",
+    )
+
+    errors = vdl.validate_file(src)
+    assert errors == []
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