From ae48798f3bbaa8c5eac5968d60ae411c37dabbb5 Mon Sep 17 00:00:00 2001
From: "Michael B. Gale" <mbg@github.com>
Date: Tue, 14 Jul 2026 15:48:57 +0100
Subject: [PATCH] Make `versions.ts` testable and add basic tests

---
 pr-checks/update-release-branch.ts | 28 +++++++++++++++----
 pr-checks/versions.test.ts         | 44 ++++++++++++++++++++++++++++++
 pr-checks/versions.ts              | 38 ++++++++++++++++----------
 3 files changed, 90 insertions(+), 20 deletions(-)
 create mode 100755 pr-checks/versions.test.ts

diff --git a/pr-checks/update-release-branch.ts b/pr-checks/update-release-branch.ts
index d6cc7670a..56f3aef31 100755
--- a/pr-checks/update-release-branch.ts
+++ b/pr-checks/update-release-branch.ts
@@ -24,7 +24,11 @@ import { parseArgs } from "node:util";
 import { type ApiClient, getApiClient } from "./api-client";
 import * as changelog from "./changelog";
 import { DryRunOption, REPO_ROOT } from "./config";
-import { getCurrentVersion, replaceVersionInPackageJson } from "./versions";
+import {
+  getCurrentVersion,
+  replaceVersionInPackageJson,
+  withPackageJson,
+} from "./versions";
 
 /**
  * NB: This exact commit message is used to find commits for reverting during backports.
@@ -636,10 +640,20 @@ export async function prepareNewBranch(
 
     // Migrate the package version number.
     console.log(`Setting version number to '${version}' in package.json`);
-    const currentPkgVersion = getCurrentVersion();
-    if (currentPkgVersion) {
-      replaceVersionInPackageJson(options, currentPkgVersion, version);
-    }
+    withPackageJson((content) => {
+      const currentPkgVersion = getCurrentVersion(content);
+      if (currentPkgVersion) {
+        return {
+          content: replaceVersionInPackageJson(
+            currentPkgVersion,
+            version,
+            content,
+          ),
+          value: currentPkgVersion,
+        };
+      }
+      return { value: currentPkgVersion };
+    }, options);
     runGit(["add", "package.json"], {
       dryRun: options.dryRun,
     });
@@ -733,7 +747,9 @@ async function main(): Promise<void> {
     "",
   );
 
-  const currentVersion = getCurrentVersion();
+  const currentVersion = withPackageJson((content) => {
+    return { value: getCurrentVersion(content) };
+  }, options);
 
   if (!currentVersion) {
     throw new Error("Failed to read current version from package.json");
diff --git a/pr-checks/versions.test.ts b/pr-checks/versions.test.ts
new file mode 100755
index 000000000..6697710f8
--- /dev/null
+++ b/pr-checks/versions.test.ts
@@ -0,0 +1,44 @@
+#!/usr/bin/env npx tsx
+
+/**
+ * Tests for `versions.ts`.
+ */
+
+import * as assert from "node:assert/strict";
+import { describe, it } from "node:test";
+
+import { getCurrentVersion, replaceVersionInPackageJson } from "./versions";
+
+describe("getCurrentVersion", async () => {
+  await it("reads versions", async () => {
+    const result = getCurrentVersion(`{ "version": "1.23.4" }`);
+    assert.deepEqual(result, "1.23.4");
+  });
+});
+
+const packageJsonContents = `{
+  "name": "codeql",
+  "version": "1.23.4"
+}
+`;
+
+const packageJsonContentsExpected = `{
+  "name": "codeql",
+  "version": "2.23.4"
+}
+`;
+
+describe("replaceVersionInPackageJson", async () => {
+  await it("replaces versions", async () => {
+    const result = replaceVersionInPackageJson(
+      "1.23.4",
+      "2.23.4",
+      packageJsonContents,
+    );
+    assert.deepEqual(
+      result.split("\n"),
+      packageJsonContentsExpected.split("\n"),
+    );
+    assert.deepEqual(JSON.parse(result), { name: "codeql", version: "2.23.4" });
+  });
+});
diff --git a/pr-checks/versions.ts b/pr-checks/versions.ts
index 359868350..4abc7faa1 100644
--- a/pr-checks/versions.ts
+++ b/pr-checks/versions.ts
@@ -2,11 +2,27 @@ import * as fs from "node:fs";
 
 import { DryRunOption, PACKAGE_JSON } from "./config";
 
+export function withPackageJson<T>(
+  transformer: (content: string) => { value: T; content?: string },
+  options: DryRunOption,
+): T {
+  const content = fs.readFileSync(PACKAGE_JSON, "utf8");
+  const result = transformer(content);
+
+  if (result.content !== undefined) {
+    if (!options.dryRun) {
+      fs.writeFileSync(PACKAGE_JSON, result.content, "utf8");
+    } else {
+      console.info(`[DRY RUN] Would have written an updated package.json`);
+    }
+  }
+
+  return result.value;
+}
+
 /** Reads the current version from `package.json`. */
-export function getCurrentVersion(): string | undefined {
-  const pkg: { version: string } = JSON.parse(
-    fs.readFileSync(PACKAGE_JSON, "utf8"),
-  );
+export function getCurrentVersion(content: string): string | undefined {
+  const pkg: { version: string } = JSON.parse(content);
   return pkg.version;
 }
 
@@ -17,11 +33,11 @@ export function getCurrentVersion(): string | undefined {
  * replace the version in package.json textually.
  */
 export function replaceVersionInPackageJson(
-  options: DryRunOption,
   prevVersion: string,
   newVersion: string,
-): void {
-  const lines = fs.readFileSync(PACKAGE_JSON, "utf8").split("\n");
+  content: string,
+): string {
+  const lines = content.split("\n");
   let prevLineIsCodeql = false;
   const output: string[] = [];
 
@@ -34,11 +50,5 @@ export function replaceVersionInPackageJson(
     prevLineIsCodeql = line.includes('"name": "codeql",');
   }
 
-  if (!options.dryRun) {
-    fs.writeFileSync(PACKAGE_JSON, `${output.join("\n")}\n`, "utf8");
-  } else {
-    console.info(
-      `[DRY RUN] Would have replaced '${prevVersion}' with '${newVersion}' in package.json`,
-    );
-  }
+  return output.join("\n");
 }