Add test for pruning on install when mirror pruning has been enabled

__tests__/commands/install/integration.js

@@ -1039,3 +1039,16 @@ test.concurrent(
   async (): Promise<void> => {
     await runInstall({}, 'relative-symlinks-work', () => {});
   });
+
+test.concurrent('prunes the offline mirror after pruning is enabled', (): Promise<void> => {
+  return runInstall({}, 'prune-offline-mirror', async (config): Promise<void> => {
+    const mirrorPath = 'mirror-for-offline';
+    // Scenario:
+    // dep-a 1.0.0 was originally installed, and it depends on dep-b 1.0.0, so
+    // both of these were added to the offline mirror. Then dep-a was upgraded
+    // to 1.1.0 which doesn't depend on dep-b. After this, pruning was enabled,
+    // so the next install should remove dep-a-1.0.0.tgz and dep-b-1.0.0.tgz.
+    assert(!await fs.exists(path.join(config.cwd, `${mirrorPath}/dep-a-1.0.0.tgz`)));
+    assert(!await fs.exists(path.join(config.cwd, `${mirrorPath}/dep-b-1.0.0.tgz`)));
+  });
+});

__tests__/fixtures/install/prune-offline-mirror/.yarnrc

@@ -0,0 +1,6 @@
+# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
+# yarn lockfile v1
+
+
+yarn-offline-mirror "./mirror-for-offline"
+yarn-offline-mirror-pruning true

__tests__/fixtures/install/prune-offline-mirror/package.json

@@ -0,0 +1,5 @@
+{
+  "dependencies": {
+    "dep-a": "1.1.0"
+  }
+}

__tests__/fixtures/install/prune-offline-mirror/yarn.lock

@@ -0,0 +1,7 @@
+# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
+# yarn lockfile v1
+
+
+dep-a@1.1.0:
+  version "1.1.0"
+  resolved dep-a-1.1.0.tgz#a347d002113da949bd89b6b71195ec3bca09db7a