chore(core): verify stack artifacts are written in topological order

packages/@aws-cdk/core/test/test.app.ts

@@ -325,6 +325,32 @@ export = {
 
     test.done();
   },
+
+  'stacks are written to the assembly file in a topological order'(test: Test) {
+    // WHEN
+    const assembly = withApp({}, (app) => {
+      const stackC = new Stack(app, 'StackC');
+      const stackD = new Stack(app, 'StackD');
+      const stackA = new Stack(app, 'StackA');
+      const stackB = new Stack(app, 'StackB');
+
+      // Create the following dependency order:
+      // A ->
+      //      C -> D
+      // B ->
+      stackC.addDependency(stackA);
+      stackC.addDependency(stackB);
+      stackD.addDependency(stackC);
+    });
+
+    // THEN
+    const artifactsIds = assembly.artifacts.map(a => a.id);
+    test.ok(artifactsIds.indexOf('StackA') < artifactsIds.indexOf('StackC'));
+    test.ok(artifactsIds.indexOf('StackB') < artifactsIds.indexOf('StackC'));
+    test.ok(artifactsIds.indexOf('StackC') < artifactsIds.indexOf('StackD'));
+
+    test.done();
+  },
 };
 
 class MyConstruct extends Construct {

packages/@aws-cdk/cx-api/test/cloud-assembly-builder.test.ts

@@ -166,4 +166,62 @@ test('write and read nested cloud assembly artifact', () => {
 
   const nested = art?.nestedAssembly;
   expect(nested?.artifacts.length).toEqual(0);
+});
+
+test('artifcats are written in topological order', () => {
+  // GIVEN
+  const outdir = fs.mkdtempSync(path.join(os.tmpdir(), 'cloud-assembly-builder-tests'));
+  const session = new cxapi.CloudAssemblyBuilder(outdir);
+  const templateFile = 'foo.template.json';
+
+  const innerAsmDir = path.join(outdir, 'hello');
+  new cxapi.CloudAssemblyBuilder(innerAsmDir).buildAssembly();
+
+  // WHEN
+
+  // Create the following dependency order:
+  // A ->
+  //      C -> D
+  // B ->
+  session.addArtifact('artifact-D', {
+    type: cxschema.ArtifactType.AWS_CLOUDFORMATION_STACK,
+    environment: 'aws://1222344/us-east-1',
+    dependencies: ['artifact-C'],
+    properties: {
+      templateFile,
+    },
+  });
+
+  session.addArtifact('artifact-C', {
+    type: cxschema.ArtifactType.AWS_CLOUDFORMATION_STACK,
+    environment: 'aws://1222344/us-east-1',
+    dependencies: ['artifact-B', 'artifact-A'],
+    properties: {
+      templateFile,
+    },
+  });
+
+  session.addArtifact('artifact-B', {
+    type: cxschema.ArtifactType.AWS_CLOUDFORMATION_STACK,
+    environment: 'aws://1222344/us-east-1',
+    properties: {
+      templateFile,
+    },
+  });
+
+  session.addArtifact('artifact-A', {
+    type: cxschema.ArtifactType.AWS_CLOUDFORMATION_STACK,
+    environment: 'aws://1222344/us-east-1',
+    properties: {
+      templateFile,
+    },
+  });
+
+  const asm = session.buildAssembly();
+  const artifactsIds = asm.artifacts.map(a => a.id);
+
+  // THEN
+  expect(artifactsIds.indexOf('artifact-A')).toBeLessThan(artifactsIds.indexOf('artifact-C'));
+  expect(artifactsIds.indexOf('artifact-B')).toBeLessThan(artifactsIds.indexOf('artifact-C'));
+  expect(artifactsIds.indexOf('artifact-C')).toBeLessThan(artifactsIds.indexOf('artifact-D'));
 });

packages/@aws-cdk/cx-api/test/cloud-assembly.test.ts

@@ -85,7 +85,7 @@ test('assets', () => {
 test('can-read-0.36.0', () => {
   // WHEN
   new CloudAssembly(path.join(FIXTURES, 'single-stack-0.36'));
-  // THEN: no eexception
+  // THEN: no exception
   expect(true).toBeTruthy();
 });