refator(backend-common): extract test utilities to plugin api

Signed-off-by: Camila Belo <camilaibs@gmail.com>

packages/backend-plugin-api/api-report-testUtils.md

@@ -0,0 +1,26 @@
+## API Report File for "@backstage/backend-plugin-api"
+
+> Do not edit this file. It is a report generated by [API Extractor](https://api-extractor.com/).
+
+```ts
+// @public
+export function overridePackagePathResolution(
+  options: OverridePackagePathResolutionOptions,
+): PackagePathResolutionOverride;
+
+// @public (undocumented)
+export interface OverridePackagePathResolutionOptions {
+  packageName: string;
+  path?: string;
+  paths?: {
+    [path in string]: string | (() => string);
+  };
+}
+
+// @public (undocumented)
+export interface PackagePathResolutionOverride {
+  restore(): void;
+}
+
+// (No @packageDocumentation comment for this package)
+```

packages/backend-plugin-api/package.json

@@ -21,6 +21,7 @@
   "exports": {
     ".": "./src/index.ts",
     "./alpha": "./src/alpha.ts",
+    "./testUtils": "./src/testUtils.ts",
     "./package.json": "./package.json"
   },
   "main": "src/index.ts",
@@ -30,6 +31,9 @@
       "alpha": [
         "src/alpha.ts"
       ],
+      "testUtils": [
+        "src/testUtils.ts"
+      ],
       "package.json": [
         "package.json"
       ]

packages/backend-plugin-api/src/testUtils.ts

@@ -0,0 +1,81 @@
+/*
+ * Copyright 2023 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.
+ */
+
+// TODO: Remove this relative import when extrating the path utilities to this package
+// eslint-disable-next-line @backstage/no-relative-monorepo-imports
+import { packagePathMocks } from '../../backend-common/src/paths';
+import { posix as posixPath, resolve as resolvePath } from 'path';
+
+/** @public */
+export interface PackagePathResolutionOverride {
+  /** Restores the normal behavior of resolvePackagePath */
+  restore(): void;
+}
+
+/** @public */
+export interface OverridePackagePathResolutionOptions {
+  /** The name of the package to mock the resolved path of */
+  packageName: string;
+
+  /** A replacement for the root package path */
+  path?: string;
+
+  /**
+   * Replacements for package sub-paths, each key must be an exact match of the posix-style path
+   * that is being resolved within the package.
+   *
+   * For example, code calling `resolvePackagePath('x', 'foo', 'bar')` would match only the following
+   * configuration: `overridePackagePathResolution({ packageName: 'x', paths: { 'foo/bar': baz } })`
+   */
+  paths?: { [path in string]: string | (() => string) };
+}
+
+/**
+ * This utility helps you override the paths returned by `resolvePackagePath` for a given package.
+ *
+ * @public
+ */
+export function overridePackagePathResolution(
+  options: OverridePackagePathResolutionOptions,
+): PackagePathResolutionOverride {
+  const name = options.packageName;
+
+  if (packagePathMocks.has(name)) {
+    throw new Error(
+      `Tried to override resolution for '${name}' more than once for package '${name}'`,
+    );
+  }
+
+  packagePathMocks.set(name, paths => {
+    const joinedPath = posixPath.join(...paths);
+    const localResolver = options.paths?.[joinedPath];
+    if (localResolver) {
+      return typeof localResolver === 'function'
+        ? localResolver()
+        : localResolver;
+    }
+    if (options.path) {
+      return resolvePath(options.path, ...paths);
+    }
+    return undefined;
+  });
+
+  return {
+    restore() {
+      packagePathMocks.delete(name);
+    },
+  };
+}