Cleanups some tests (#6388)

## What's the problem this PR addresses?

I'm reviewing our tests and came upon some of them that could be dumbed
down. I prefer to make them test as little things as possible to avoid
something breaking due to unrelated parts of the code changing (I'm
working on switching some implementations, and limiting test
dependencies make things considerably easier / more fun to work on).

## How did you fix it?


No big changes - it's mostly things like using the `dependencies` rather
than calling `yarn add` and avoiding to rely on cache paths to check
whether something got properly installed.

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packages/acceptance-tests/pkg-tests-core/sources/utils/exec.ts

@@ -8,6 +8,7 @@ export const execPromise = promisify(exec);
 interface Options {
   cwd: PortablePath;
   env?: Record<string, string>;
+  stdin?: string;
 }
 
 export type ExecResult = {
@@ -25,7 +26,7 @@ export const execFile = (
   options: Options,
 ): Promise<ExecResult> => {
   return new Promise((resolve, reject) => {
-    cp.execFile(path, args, {
+    const process = cp.execFile(path, args, {
       ...options,
       cwd: options.cwd ? npath.fromPortablePath(options.cwd) : undefined,
     }, (error, stdout, stderr) => {
@@ -50,6 +51,11 @@ export const execFile = (
         });
       }
     });
+
+    if (typeof options.stdin !== `undefined`) {
+      process.stdin?.write(options.stdin);
+      process.stdin?.end();
+    }
   });
 };
 

packages/acceptance-tests/pkg-tests-core/sources/utils/makeTemporaryEnv.ts

@@ -14,7 +14,7 @@ const mte = generatePkgDriver({
   async runDriver(
     path,
     [command, ...args],
-    {cwd, execArgv = [], projectFolder, registryUrl, env, ...config},
+    {cwd, execArgv = [], projectFolder, registryUrl, env, stdin, ...config},
   ) {
     const rcEnv: Record<string, any> = {};
     for (const [key, value] of Object.entries(config))
@@ -32,6 +32,7 @@ const mte = generatePkgDriver({
 
     const res = await execFile(process.execPath, [...execArgv, yarnBinary, ...cwdArgs, command, ...args], {
       cwd: cwd || path,
+      stdin,
       env: {
         [`HOME`]: nativeHomePath,
         [`USERPROFILE`]: nativeHomePath,

packages/acceptance-tests/pkg-tests-core/sources/utils/tests.ts

@@ -38,6 +38,7 @@ interface RunDriverOptions extends Record<string, any> {
   projectFolder?: PortablePath;
   registryUrl: string;
   env?: Record<string, string | undefined>;
+  stdin?: string;
 }
 
 export type PackageRunDriver = (

packages/acceptance-tests/pkg-tests-specs/sources/node-modules.test.ts

@@ -1871,7 +1871,7 @@ describe(`Node_Modules`, () => {
           },
         });
 
-        await expect(run(`install`)).resolves.toMatchObject({code: 0});
+        await run(`install`);
 
         await expect(xfs.readdirPromise(ppath.join(path, Filename.nodeModules))).resolves.toEqual([
           `.yarn-state.yml`,