fix: gather-versions doesn't work for >= 2 dependencies (#833)

* fix: gather-versions doesn't work for 0 or 1 dependencies

When I simplified the command-line that `gather-versions` takes, I
forgot to take out the condition that requires a minimum number of
arguments.

The result is that `gather-versions` won't do anything thing for
packages that have 0 or 1 workspace dependency; plus, the script didn't
actually exit with an error code when that happened, so it was hard to
detect.

Fix that in this PR, and also add a test that runs the `gather-versions`
task properly from a projen monorepo config using `TaskRuntime`.

* fix: gather-versions doesn't work for >= 2 dependencies

During refactoring I accidentally removed a `.join(' ')` so an
array stringifies fine but stringifies to the wrong string. Instead of:

```
a b c
```

it stringifies to

```
a,b,c
```

Which is not a command-line argument per package, but once command-line
argument with all packages in there.

Author: rix0rrr

src/yarn/gather-versions.task.ts

@@ -34,7 +34,7 @@ export class GatherVersions implements TaskOptions, TaskStep {
   public get exec(): string {
     // We must resolve paths at runtime to avoid writing '/home/$USER/...' into the `tasks.json` file
     const main = `require(require.resolve('${currentPackageName()}/lib/yarn/gather-versions.exec.js')).cliMain()`;
-    return `node -e "${main}" ${Object.entries(this.repoDependencies).map(([d, r]) => `${d}=${r}`)}`;
+    return `node -e "${main}" ${Object.entries(this.repoDependencies).map(([d, r]) => `${d}=${r}`).join(' ')}`;
   }
 
   public toJSON() {

test/gather-versions.test.ts

@@ -64,25 +64,27 @@ const NO_DEVDEPS: Partial<TypeScriptWorkspaceOptions> = {
   prettier: false,
 };
 
-test('make sure a run of gather-versions writes the right version to package.json', async () => {
+test.each([0, 1, 2])('make sure gather-versions works for %p dependencies', async (N) => {
   // GIVEN
   const parent = new yarn.CdkLabsMonorepo({
     name: 'monorepo',
     defaultReleaseBranch: 'main',
     release: true,
   });
-
-  const dep = new yarn.TypeScriptWorkspace({
-    parent,
-    name: '@cdklabs/one',
-    ...NO_DEVDEPS,
-  });
+  let deps: yarn.TypeScriptWorkspace[] = [];
+  for (let i = 0; i < N; i++) {
+    deps.push(new yarn.TypeScriptWorkspace({
+      parent,
+      name: `@cdklabs/dep${i}`,
+      ...NO_DEVDEPS,
+    }));
+  }
 
   // WHEN
   const pack = new yarn.TypeScriptWorkspace({
     parent,
     name: '@cdklabs/two',
-    deps: [dep.customizeReference({ versionType: 'exact' })],
+    deps: deps.map(dep => dep.customizeReference({ versionType: 'exact' })),
     ...NO_DEVDEPS,
   });
 
@@ -93,9 +95,11 @@ test('make sure a run of gather-versions writes the right version to package.jso
   new TaskRuntime(pack.outdir).runTask('gather-versions');
 
   const packageJson = JSON.parse(await fs.readFile(path.join(pack.outdir, 'package.json'), 'utf-8'));
-  expect(Object.entries(packageJson.dependencies)).toContainEqual([
-    '@cdklabs/one', '0.0.0',
-  ]);
+  for (let i = 0; i < N; i++) {
+    expect(Object.entries(packageJson.dependencies)).toContainEqual([
+      `@cdklabs/dep${i}`, '0.0.0',
+    ]);
+  }
 }, 60_000); // Needs to install real packages
 
 /**