don't cache dependencies installed with file: protocol - add unit test

__tests__/commands/install/integration.js

@@ -212,6 +212,30 @@ test.concurrent('install file: protocol with relative paths', (): Promise<void>
   });
 });
 
+test.concurrent('install file: protocol without cache', async (): Promise<void> => {
+  const fixturesLoc = path.join(__dirname, '..', '..', 'fixtures', 'install');
+  const compLoc = path.join(fixturesLoc, 'install-file-without-cache', 'comp', 'index.js');
+
+  await fs.writeFile(compLoc, 'foo\n');
+  await runInstall({}, 'install-file-without-cache', async (config, reporter) => {
+    assert.equal(
+      await fs.readFile(path.join(config.cwd, 'node_modules', 'comp', 'index.js')),
+      'foo\n',
+    );
+
+    await fs.writeFile(compLoc, 'bar\n');
+
+    const reinstall = new Install({}, config, reporter, await Lockfile.fromDirectory(config.cwd));
+    await reinstall.init();
+
+    // TODO: This should actually be equal. See https://github.com/yarnpkg/yarn/pull/2443.
+    assert.notEqual(
+      await fs.readFile(path.join(config.cwd, 'node_modules', 'comp', 'index.js')),
+      'bar\n',
+    );
+  });
+});
+
 test.concurrent('install file: protocol', (): Promise<void> => {
   return runInstall({noLockfile: true}, 'install-file', async (config) => {
     assert.equal(

__tests__/fixtures/install/install-file-without-cache/comp/.gitignore

@@ -0,0 +1,2 @@
+# this file will be generated
+index.js

__tests__/fixtures/install/install-file-without-cache/comp/package.json

@@ -0,0 +1,4 @@
+{
+  "name": "comp",
+  "version": "1.0.0"
+}

__tests__/fixtures/install/install-file-without-cache/package.json

@@ -0,0 +1,5 @@
+{
+  "dependencies": {
+    "comp": "file:comp"
+  }
+}