test(price-pusher): add unit tests for readMnemonic + bump minor

Per review feedback:

- Bump @pythnetwork/price-pusher to 10.5.0 (minor) — backward-compatible
  feature addition (MNEMONIC env var fallback). 10.4.0 was consumed by
  #3687 hermes-access-token.
- Add tests/utils.test.ts covering all three readMnemonic paths plus
  the file-precedence-over-env behaviour: file source, env fallback,
  empty-string path (treated as not supplied), file > env precedence,
  missing-both error, empty-env error.
- Wire `test:unit` script into apps/price_pusher/package.json so the
  workspace runner picks it up.

`pnpm --filter @pythnetwork/price-pusher exec test-unit` — 6 passing.

Author: 0xghost42

apps/price_pusher/package.json

@@ -215,9 +215,10 @@
     "dev": "ts-node src/index.ts",
     "prepublishOnly": "pnpm run build",
     "start": "node dist/index.cjs",
-    "test:types": "tsc"
+    "test:types": "tsc",
+    "test:unit": "test-unit"
   },
   "type": "module",
   "types": "./dist/index.d.ts",
-  "version": "10.4.0"
+  "version": "10.5.0"
 }

apps/price_pusher/tests/utils.test.ts

@@ -0,0 +1,62 @@
+// biome-ignore-all lint/style/noProcessEnv: test file manipulates env vars
+
+import { mkdtempSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+
+import { readMnemonic } from "../src/utils.js";
+
+describe("readMnemonic", () => {
+  let tmpDir: string;
+  const originalMnemonic = process.env.MNEMONIC;
+
+  beforeEach(() => {
+    tmpDir = mkdtempSync(join(tmpdir(), "price-pusher-test-"));
+    delete process.env.MNEMONIC;
+  });
+
+  afterEach(() => {
+    rmSync(tmpDir, { recursive: true, force: true });
+    if (originalMnemonic === undefined) {
+      delete process.env.MNEMONIC;
+    } else {
+      process.env.MNEMONIC = originalMnemonic;
+    }
+  });
+
+  it("reads mnemonic from file when path supplied", () => {
+    const path = join(tmpDir, "mnemonic");
+    writeFileSync(path, "from file mnemonic\n");
+    expect(readMnemonic(path)).toBe("from file mnemonic");
+  });
+
+  it("falls back to MNEMONIC env var when no file path supplied", () => {
+    process.env.MNEMONIC = "from env mnemonic";
+    expect(readMnemonic(undefined)).toBe("from env mnemonic");
+  });
+
+  it("treats empty-string file path as not supplied", () => {
+    process.env.MNEMONIC = "from env mnemonic";
+    expect(readMnemonic("")).toBe("from env mnemonic");
+  });
+
+  it("file source takes precedence over env var", () => {
+    const path = join(tmpDir, "mnemonic");
+    writeFileSync(path, "from file\n");
+    process.env.MNEMONIC = "from env";
+    expect(readMnemonic(path)).toBe("from file");
+  });
+
+  it("throws when neither file nor env var supplied", () => {
+    expect(() => readMnemonic(undefined)).toThrow(
+      /No mnemonic provided/,
+    );
+  });
+
+  it("throws when env var is empty string", () => {
+    process.env.MNEMONIC = "";
+    expect(() => readMnemonic(undefined)).toThrow(
+      /No mnemonic provided/,
+    );
+  });
+});