diff --git a/tools/hygiene/check-tick-history-shard-schema.test.ts b/tools/hygiene/check-tick-history-shard-schema.test.ts
new file mode 100644
index 000000000..3e8142cbd
--- /dev/null
+++ b/tools/hygiene/check-tick-history-shard-schema.test.ts
@@ -0,0 +1,112 @@
+import { afterAll, beforeAll, describe, expect, test } from "bun:test";
+import { mkdirSync, mkdtempSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { dirname, join } from "node:path";
+
+import type { ScanResult } from "./check-tick-history-shard-schema";
+
+type ScanOne = (shardPath: string) => ScanResult;
+
+let TMPDIR: string;
+let scanOne: ScanOne;
+let priorRepoRoot: string | undefined;
+
+beforeAll(async () => {
+  TMPDIR = mkdtempSync(join(tmpdir(), "shard-schema-test-"));
+  priorRepoRoot = process.env["REPO_ROOT"];
+  process.env["REPO_ROOT"] = TMPDIR;
+  const mod = await import("./check-tick-history-shard-schema");
+  scanOne = mod.scanOne;
+});
+
+afterAll(() => {
+  if (priorRepoRoot === undefined) delete process.env["REPO_ROOT"];
+  else process.env["REPO_ROOT"] = priorRepoRoot;
+  if (TMPDIR) rmSync(TMPDIR, { recursive: true, force: true });
+});
+
+function writeShard(relPath: string, content: string): string {
+  const full = join(TMPDIR, "docs/hygiene-history/ticks", relPath);
+  mkdirSync(dirname(full), { recursive: true });
+  writeFileSync(full, content);
+  return full;
+}
+
+const SIX_COLS = "| 2026-05-17T12:34Z | a | b | c | d | e |\n";
+
+describe("scanOne", () => {
+  test("accepts a valid HHMMZ.md shard", () => {
+    const path = writeShard("2026/05/17/1234Z.md", SIX_COLS);
+    const result = scanOne(path);
+
+    expect(result.ok).toBe(true);
+    expect(result.violation).toBeUndefined();
+  });
+
+  test("accepts HHMMZ-<hex>.md filename variant", () => {
+    const path = writeShard("2026/05/17/1234Z-abc123.md", SIX_COLS);
+    const result = scanOne(path);
+
+    expect(result.ok).toBe(true);
+  });
+
+  test("accepts col1 with seconds (HH:MM:SSZ) when minutes match filename", () => {
+    const content = "| 2026-05-17T12:34:56Z | a | b | c | d | e |\n";
+    const path = writeShard("2026/05/17/1234Z.md", content);
+    const result = scanOne(path);
+
+    expect(result.ok).toBe(true);
+  });
+
+  test("flags filename that does not match any schema regex", () => {
+    const path = writeShard("2026/05/17/foo.md", SIX_COLS);
+    const result = scanOne(path);
+
+    expect(result.ok).toBe(false);
+    expect(result.violation).toContain("filename does not match");
+  });
+
+  test("flags col1 date mismatch with path date", () => {
+    const content = "| 2026-05-18T12:34Z | a | b | c | d | e |\n";
+    const path = writeShard("2026/05/17/1234Z.md", content);
+    const result = scanOne(path);
+
+    expect(result.ok).toBe(false);
+    expect(result.violation).toContain("does not match path date");
+  });
+
+  test("flags col1 time mismatch with filename time", () => {
+    const content = "| 2026-05-17T12:35Z | a | b | c | d | e |\n";
+    const path = writeShard("2026/05/17/1234Z.md", content);
+    const result = scanOne(path);
+
+    expect(result.ok).toBe(false);
+    expect(result.violation).toContain("does not match filename");
+  });
+
+  test("flags first row with fewer than 6 columns (7+ pipes)", () => {
+    const content = "| 2026-05-17T12:34Z | only one col |\n";
+    const path = writeShard("2026/05/17/1234Z.md", content);
+    const result = scanOne(path);
+
+    expect(result.ok).toBe(false);
+    expect(result.violation).toContain("pipes");
+  });
+
+  test("flags empty file", () => {
+    const path = writeShard("2026/05/17/1234Z.md", "");
+    const result = scanOne(path);
+
+    expect(result.ok).toBe(false);
+    expect(result.violation).toBe("file is empty");
+  });
+
+  test("flags col1 missing leading pipe-space-timestamp format", () => {
+    const content = "|2026-05-17T12:34Z | a | b | c | d | e |\n";
+    const path = writeShard("2026/05/17/1234Z.md", content);
+    const result = scanOne(path);
+
+    expect(result.ok).toBe(false);
+    expect(result.violation).toContain("col1 must be exactly");
+  });
+});
diff --git a/tools/hygiene/check-tick-history-shard-schema.ts b/tools/hygiene/check-tick-history-shard-schema.ts
index c08905e86..e539d5d10 100644
--- a/tools/hygiene/check-tick-history-shard-schema.ts
+++ b/tools/hygiene/check-tick-history-shard-schema.ts
@@ -35,7 +35,7 @@ const HASH_RE = /^(\d{4})(\d{2})Z-[0-9a-f]+$/;
 const COL1_RE = /^\|\s(\d{4}-\d{2}-\d{2}T\d{2}:\d{2}(?::\d{2})?Z)\s\|\s/;
 const SHARD_PREFIX = "docs/hygiene-history/ticks/";
 
-interface ScanResult {
+export interface ScanResult {
   path: string;
   ok: boolean;
   violation?: string;
@@ -49,7 +49,7 @@ function repoRelative(p: string): string {
   return normalizeToPosix(relative(ROOT, p));
 }
 
-function scanOne(shardPath: string): ScanResult {
+export function scanOne(shardPath: string): ScanResult {
   const pathRel = repoRelative(resolve(ROOT, shardPath));
   const base = basename(shardPath, ".md");