diff --git a/packages/aws-cdk/lib/api/cxapp/cloud-assembly.ts b/packages/aws-cdk/lib/api/cxapp/cloud-assembly.ts
index 3e88e64cfc7dc..3bc37117162d6 100644
--- a/packages/aws-cdk/lib/api/cxapp/cloud-assembly.ts
+++ b/packages/aws-cdk/lib/api/cxapp/cloud-assembly.ts
@@ -345,7 +345,6 @@ function includeDownstreamStacks(
   } while (madeProgress);
 
   if (added.length > 0) {
-    // @todo remove here or use iohost
     info('Including depending stacks: %s', chalk.bold(added.join(', ')));
   }
 }
@@ -376,7 +375,6 @@ function includeUpstreamStacks(
   }
 
   if (added.length > 0) {
-    // @todo remove here or use iohost
     info('Including dependency stacks: %s', chalk.bold(added.join(', ')));
   }
 }
diff --git a/packages/aws-cdk/test/api/cloud-assembly.test.ts b/packages/aws-cdk/test/api/cloud-assembly.test.ts
index ce66be6a9a0a0..574b401b9d30c 100644
--- a/packages/aws-cdk/test/api/cloud-assembly.test.ts
+++ b/packages/aws-cdk/test/api/cloud-assembly.test.ts
@@ -4,33 +4,6 @@ import { DefaultSelection } from '../../lib/api/cxapp/cloud-assembly';
 import { MockCloudExecutable } from '../util';
 import { cliAssemblyWithForcedVersion } from './assembly-versions';
 
-test('do not throw when selecting stack without errors', async () => {
-  // GIVEN
-  const cxasm = await testCloudAssembly();
-
-  // WHEN
-  const selected = await cxasm.selectStacks( { patterns: ['withouterrorsNODEPATH'] }, {
-    defaultBehavior: DefaultSelection.AllStacks,
-  });
-  await selected.validateMetadata();
-
-  // THEN
-  expect(selected.firstStack.template.resource).toBe('noerrorresource');
-});
-
-test('do throw when selecting stack with errors', async () => {
-  // GIVEN
-  const cxasm = await testCloudAssembly();
-
-  // WHEN
-  const selected = await cxasm.selectStacks({ patterns: ['witherrors'] }, {
-    defaultBehavior: DefaultSelection.AllStacks,
-  });
-
-  // THEN
-  await expect(async () => selected.validateMetadata()).rejects.toThrow(/Found errors/);
-});
-
 test('select all top level stacks in the presence of nested assemblies', async () => {
   // GIVEN
   const cxasm = await testNestedCloudAssembly();
@@ -186,6 +159,95 @@ test('select behavior with no stacks and default ignore stacks options (false)',
     .rejects.toThrow('This app contains no stacks');
 });
 
+describe('StackCollection', () => {
+  test('returns hierarchicalIds', async () => {
+    // GIVEN
+    const cxasm = await testNestedCloudAssembly();
+
+    // WHEN
+    const x = await cxasm.selectStacks({ allTopLevel: true, patterns: [] }, { defaultBehavior: DefaultSelection.AllStacks });
+
+    // THEN
+    expect(x.stackCount).toBe(2);
+    expect(x.hierarchicalIds).toEqual(['witherrors', 'deeply/hidden/withouterrors']);
+  });
+
+  describe('validateMetadata', () => {
+    test('do not throw when selecting stack without errors', async () => {
+    // GIVEN
+      const cxasm = await testCloudAssembly();
+
+      // WHEN
+      const selected = await cxasm.selectStacks( { patterns: ['withouterrorsNODEPATH'] }, {
+        defaultBehavior: DefaultSelection.AllStacks,
+      });
+      await selected.validateMetadata();
+
+      // THEN
+      expect(selected.stackCount).toBe(1);
+      expect(selected.firstStack.template.resource).toBe('noerrorresource');
+    });
+
+    test('do not throw when selecting stack with warnings', async () => {
+      // GIVEN
+      const cxasm = await testCloudAssembly();
+
+      // WHEN
+      const selected = await cxasm.selectStacks( { patterns: ['withwarns'] }, {
+        defaultBehavior: DefaultSelection.AllStacks,
+      });
+      await selected.validateMetadata();
+
+      // THEN
+      expect(selected.stackCount).toBe(1);
+      expect(selected.firstStack.template.resource).toBe('warnresource');
+    });
+
+    test('do not throw when selecting stack with errors but errors are ignored', async () => {
+      // GIVEN
+      const cxasm = await testCloudAssembly();
+
+      // WHEN
+      const selected = await cxasm.selectStacks({ patterns: ['witherrors'] }, {
+        defaultBehavior: DefaultSelection.AllStacks,
+      });
+      await selected.validateMetadata('none');
+
+      // THEN
+      expect(selected.stackCount).toBe(1);
+      expect(selected.firstStack.template.resource).toBe('errorresource');
+    });
+
+    test('do throw when selecting stack with errors', async () => {
+      // GIVEN
+      const cxasm = await testCloudAssembly();
+
+      // WHEN
+      const selected = await cxasm.selectStacks({ patterns: ['witherrors'] }, {
+        defaultBehavior: DefaultSelection.AllStacks,
+      });
+
+      // THEN
+      expect(selected.stackCount).toBe(1);
+      await expect(async () => selected.validateMetadata()).rejects.toThrow(/Found errors/);
+    });
+
+    test('do throw when selecting stack with warnings and we are on strict mode', async () => {
+      // GIVEN
+      const cxasm = await testCloudAssembly();
+
+      // WHEN
+      const selected = await cxasm.selectStacks( { patterns: ['withwarns'] }, {
+        defaultBehavior: DefaultSelection.AllStacks,
+      });
+
+      // THEN
+      expect(selected.stackCount).toBe(1);
+      await expect(async () => selected.validateMetadata('warn')).rejects.toThrow(/Found warnings/);
+    });
+  });
+});
+
 async function testCloudAssembly({ env }: { env?: string; versionReporting?: boolean } = {}) {
   const cloudExec = new MockCloudExecutable({
     stacks: [{
@@ -206,6 +268,19 @@ async function testCloudAssembly({ env }: { env?: string; versionReporting?: boo
           },
         ],
       },
+    },
+    {
+      stackName: 'withwarns',
+      env,
+      template: { resource: 'warnresource' },
+      metadata: {
+        '/resource': [
+          {
+            type: cxschema.ArtifactMetadataEntryType.WARN,
+            data: 'this is a warning',
+          },
+        ],
+      },
     }],
   });
 
diff --git a/packages/aws-cdk/test/serialize.test.ts b/packages/aws-cdk/test/serialize.test.ts
index c30e3caec2715..e465f1c8f8630 100644
--- a/packages/aws-cdk/test/serialize.test.ts
+++ b/packages/aws-cdk/test/serialize.test.ts
@@ -1,5 +1,5 @@
 /* eslint-disable import/order */
-import { toYAML } from '../lib/serialize';
+import { toYAML, obscureTemplate } from '../lib/serialize';
 
 describe(toYAML, () => {
   test('does not wrap lines', () => {
@@ -7,3 +7,30 @@ describe(toYAML, () => {
     expect(toYAML({ longString })).toEqual(`longString: ${longString}\n`);
   });
 });
+
+describe(obscureTemplate, () => {
+  test('removes CheckBootstrapVersion rule only', () => {
+    const template = {
+      Rules: {
+        CheckBootstrapVersion: { Assertions: [{ AssertDescription: 'bootstrap' }] },
+        MyOtherRule: { Assertions: [{ AssertDescription: 'other' }] },
+      },
+    };
+
+    const obscured = obscureTemplate(template);
+    expect(obscured).not.toHaveProperty('Rules.CheckBootstrapVersion');
+    expect(obscured).toHaveProperty('Rules.MyOtherRule.Assertions.0.AssertDescription', 'other');
+  });
+
+  test('removes all rules when CheckBootstrapVersion is the only rule', () => {
+    const template = {
+      Rules: {
+        CheckBootstrapVersion: { Assertions: [{ AssertDescription: 'bootstrap' }] },
+      },
+    };
+
+    const obscured = obscureTemplate(template);
+    expect(obscured).not.toHaveProperty('Rules.CheckBootstrapVersion');
+    expect(obscured).not.toHaveProperty('Rules');
+  });
+});
diff --git a/packages/aws-cdk/test/toolkit-error.test.ts b/packages/aws-cdk/test/toolkit-error.test.ts
index 1aef772e186a5..5f2ff259300f1 100644
--- a/packages/aws-cdk/test/toolkit-error.test.ts
+++ b/packages/aws-cdk/test/toolkit-error.test.ts
@@ -1,17 +1,30 @@
-import { AuthenticationError, ToolkitError } from '../lib/toolkit/error';
+import { AssemblyError, AuthenticationError, ToolkitError } from '../lib/toolkit/error';
 
 describe('toolkit error', () => {
   let toolkitError = new ToolkitError('Test toolkit error');
   let authError = new AuthenticationError('Test authentication error');
+  let assemblyError = new AssemblyError('Test authentication error');
+
   test('types are correctly assigned', async () => {
     expect(toolkitError.type).toBe('toolkit');
     expect(authError.type).toBe('authentication');
+    expect(assemblyError.type).toBe('assembly');
   });
 
-  test('isToolkitError and isAuthenticationError functions work', () => {
+  test('isToolkitError works', () => {
     expect(ToolkitError.isToolkitError(toolkitError)).toBe(true);
     expect(ToolkitError.isToolkitError(authError)).toBe(true);
+    expect(ToolkitError.isToolkitError(assemblyError)).toBe(true);
+  });
+
+  test('isAuthenticationError works', () => {
     expect(ToolkitError.isAuthenticationError(toolkitError)).toBe(false);
     expect(ToolkitError.isAuthenticationError(authError)).toBe(true);
   });
+
+  test('isAssemblyError works', () => {
+    expect(ToolkitError.isAssemblyError(assemblyError)).toBe(true);
+    expect(ToolkitError.isAssemblyError(toolkitError)).toBe(false);
+    expect(ToolkitError.isAssemblyError(authError)).toBe(false);
+  });
 });
diff --git a/packages/aws-cdk/test/toolkit/cli-io-host.test.ts b/packages/aws-cdk/test/toolkit/cli-io-host.test.ts
index 910f2ad19df81..210a9a310a95e 100644
--- a/packages/aws-cdk/test/toolkit/cli-io-host.test.ts
+++ b/packages/aws-cdk/test/toolkit/cli-io-host.test.ts
@@ -239,4 +239,21 @@ describe('CliIoHost', () => {
       })).rejects.toThrow('Write failed');
     });
   });
+
+  describe('requestResponse', () => {
+    test('logs messages and returns default', async () => {
+      CliIoHost.isTTY = true;
+      const response = await CliIoHost.getIoHost().requestResponse({
+        time: new Date(),
+        level: 'info',
+        action: 'synth',
+        code: 'CDK_TOOLKIT_I0001',
+        message: 'test message',
+        defaultResponse: 'default response',
+      });
+
+      expect(mockStderr).toHaveBeenCalledWith(chalk.white('test message') + '\n');
+      expect(response).toBe('default response');
+    });
+  });
 });