i18n(labs): say why a biomarker's unit cannot change once it has readings

src/components/labs/__tests__/biomarker-form.test.tsx

@@ -0,0 +1,80 @@
+import { describe, it, expect, vi } from "vitest";
+import { renderToStaticMarkup } from "react-dom/server";
+
+import { I18nProvider } from "@/lib/i18n/context";
+import { ApiError } from "@/lib/api/api-fetch";
+import { localizedApiError } from "@/lib/api/localized-error";
+import en from "../../../../messages/en.json";
+
+/**
+ * The marker editor says, before a save, that a marker's unit stays as it is
+ * once readings exist, and the refusal the server sends for such a change
+ * reads as that sentence rather than the generic save error.
+ */
+
+vi.mock("@/lib/api/api-fetch", async (importOriginal) => ({
+  ...(await importOriginal<typeof import("@/lib/api/api-fetch")>()),
+  apiPost: vi.fn(),
+  apiPut: vi.fn(),
+}));
+
+import { BiomarkerForm } from "../biomarker-form";
+import type { BiomarkerDto } from "../types";
+
+const MARKER: BiomarkerDto = {
+  id: "bm-1",
+  name: "Glucose",
+  unit: "mg/dL",
+  lowerBound: 70,
+  upperBound: 99,
+  panel: null,
+  hasContext: false,
+  context: null,
+  hidden: false,
+  createdAt: "2026-01-01T00:00:00.000Z",
+  updatedAt: "2026-01-01T00:00:00.000Z",
+};
+
+function render(node: React.ReactNode) {
+  return renderToStaticMarkup(
+    <I18nProvider initialLocale="en">{node}</I18nProvider>,
+  );
+}
+
+describe("<BiomarkerForm> unit lock", () => {
+  const hint = en.labs.biomarker.form.unitLockedHint;
+
+  it("tells the editor of an existing marker that the unit is locked by readings", () => {
+    const html = render(<BiomarkerForm existing={MARKER} />);
+    expect(hint.length).toBeGreaterThan(0);
+    expect(html).toContain(hint.replace(/'/g, "&#x27;"));
+    expect(html).toMatch(/aria-describedby="[^"]*-unit-hint"/);
+  });
+
+  it("says nothing of a lock while a new marker is defined", () => {
+    const html = render(<BiomarkerForm />);
+    expect(html).not.toContain(hint.replace(/'/g, "&#x27;"));
+  });
+
+  it("reads the server's refusal as its own sentence, not the save error", () => {
+    const err = new ApiError("locked", 422, {
+      errorCode: "biomarkers.unit.locked",
+      readingCount: 2,
+    });
+    const t = (key: string) => {
+      const value = key
+        .split(".")
+        .reduce<unknown>(
+          (node, part) =>
+            node && typeof node === "object"
+              ? (node as Record<string, unknown>)[part]
+              : undefined,
+          en,
+        );
+      return typeof value === "string" ? value : key;
+    };
+    expect(localizedApiError(err, t, "labs.biomarker.form.saveError")).toBe(
+      en.apiErrors.biomarkers.unit.locked,
+    );
+  });
+});