yarn-plugin: refactor retrieval of workspace root portable path for testability

Signed-off-by: MT Lewis <mtlewis@users.noreply.github.com>

packages/yarn-plugin/src/util/getCurrentBackstageVersion.ts

@@ -16,15 +16,13 @@
 
 import assert from 'assert';
 import { valid as semverValid } from 'semver';
-import { npath, ppath, xfs } from '@yarnpkg/fslib';
-import { BACKSTAGE_JSON, findPaths } from '@backstage/cli-common';
+import { ppath, xfs } from '@yarnpkg/fslib';
+import { BACKSTAGE_JSON } from '@backstage/cli-common';
 import { memoize } from './memoize';
+import { getWorkspaceRoot } from './getWorkspaceRoot';
 
 export const getCurrentBackstageVersion = memoize(() => {
-  const workspaceRoot = npath.toPortablePath(
-    findPaths(npath.fromPortablePath(ppath.cwd())).targetRoot,
-  );
-  const backstageJsonPath = ppath.join(workspaceRoot, BACKSTAGE_JSON);
+  const backstageJsonPath = ppath.join(getWorkspaceRoot(), BACKSTAGE_JSON);
 
   let backstageVersion: string | null = null;
   try {

packages/yarn-plugin/src/util/getWorkspaceRoot.test.ts

@@ -0,0 +1,70 @@
+/*
+ * Copyright 2024 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { findPaths, Paths } from '@backstage/cli-common';
+
+const setPlatform = (platform: string) => {
+  Object.defineProperty(process, `platform`, {
+    configurable: true,
+    value: platform,
+  });
+};
+
+describe('getWorkspaceRoot', () => {
+  /**
+   * Yarn uses a PortablePath type which uses the posix separator
+   * regardless of platform and prefixes absolute paths with a separator.
+   *
+   * https://yarnpkg.com/api/yarnpkg-fslib#type-safe-paths
+   */
+  describe.each`
+    platform    | native                     | portable
+    ${'darwin'} | ${'/test/workspace/'}      | ${'/test/workspace/'}
+    ${'win32'}  | ${'C:\\test\\workspace\\'} | ${'/C:/test/workspace/'}
+  `('platform: $platform', ({ platform, native, portable }) => {
+    let realPlatform: string;
+    let getWorkspaceRoot: () => string;
+    let mockFindPaths: jest.MockedFunction<typeof findPaths>;
+
+    beforeEach(() => {
+      realPlatform = process.platform;
+      setPlatform(platform);
+
+      jest.resetModules();
+
+      mockFindPaths = jest.fn();
+
+      jest.doMock('@backstage/cli-common', () => ({
+        ...jest.requireActual('@backstage/cli-common'),
+        findPaths: mockFindPaths,
+      }));
+
+      getWorkspaceRoot = require('./getWorkspaceRoot').getWorkspaceRoot;
+    });
+
+    afterEach(() => {
+      setPlatform(realPlatform);
+    });
+
+    it('returns an appropriately-formatted workspace root path', () => {
+      mockFindPaths.mockReturnValue({
+        targetRoot: native,
+      } as Paths);
+
+      expect(getWorkspaceRoot()).toEqual(portable);
+    });
+  });
+});

packages/yarn-plugin/src/util/getWorkspaceRoot.ts

@@ -0,0 +1,24 @@
+/*
+ * Copyright 2024 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { npath, ppath } from '@yarnpkg/fslib';
+import { findPaths } from '@backstage/cli-common';
+
+export const getWorkspaceRoot = () => {
+  return npath.toPortablePath(
+    findPaths(npath.fromPortablePath(ppath.cwd())).targetRoot,
+  );
+};