Report the constituent errors of an AggregateError

Fixes #2063

spec/core/integration/ExceptionFormattingSpec.js

@@ -0,0 +1,84 @@
+describe('Exception formatting (integration)', function() {
+  let env;
+
+  beforeEach(function() {
+    specHelpers.registerIntegrationMatchers();
+    env = new privateUnderTest.Env();
+  });
+
+  afterEach(function() {
+    env.cleanup_();
+  });
+
+  describe('AggregateError formatting', function() {
+    it('formats AggregateError with individual errors', async function() {
+      env.it('should format AggregateError with individual errors', function() {
+        const errors = [
+          new Error('Database connection failed'),
+          new Error('Invalid configuration'),
+          new Error('Service unavailable')
+        ];
+        throw new AggregateError(errors, 'Multiple initialization errors');
+      });
+
+      const reporter = jasmine.createSpyObj('reporter', ['specDone']);
+      env.addReporter(reporter);
+      await env.execute();
+
+      expect(reporter.specDone).toHaveBeenCalledTimes(1);
+      const result = reporter.specDone.calls.argsFor(0)[0];
+      expect(result.status).toEqual('failed');
+      expect(result.failedExpectations.length).toEqual(1);
+
+      const failure = result.failedExpectations[0];
+      expect(failure.message).toContain('AggregateError');
+      expect(failure.message).toContain('Multiple initialization errors');
+
+      expect(failure.stack).toContain(
+        'Error 1: Error: Database connection failed'
+      );
+      expect(failure.stack).toContain('Error 2: Error: Invalid configuration');
+      expect(failure.stack).toContain('Error 3: Error: Service unavailable');
+    });
+
+    it('formats nested AggregateError', async function() {
+      env.it('should format nested AggregateError', function() {
+        const innerErrors = [
+          new Error('Inner error 1'),
+          new Error('Inner error 2')
+        ];
+        const innerAggregate = new AggregateError(
+          innerErrors,
+          'Inner operation failed'
+        );
+
+        const outerErrors = [
+          innerAggregate,
+          new Error('Outer error'),
+          new Error('Other outer error')
+        ];
+        throw new AggregateError(outerErrors, 'Multiple operations failed');
+      });
+
+      const reporter = jasmine.createSpyObj('reporter', ['specDone']);
+      env.addReporter(reporter);
+      await env.execute();
+
+      expect(reporter.specDone).toHaveBeenCalledTimes(1);
+      const result = reporter.specDone.calls.argsFor(0)[0];
+      expect(result.status).toEqual('failed');
+
+      const failure = result.failedExpectations[0];
+
+      // Firefox & Safari don't preserve types for nested errors
+      expect(failure.stack).toMatch(
+        /Error 1: (AggregateError|Error): Inner operation failed/
+      );
+      expect(failure.stack).toContain('Error 2: Error: Outer error');
+      expect(failure.stack).toContain('Error 3: Error: Other outer error');
+
+      expect(failure.stack).toContain('Error 1: Error: Inner error 1');
+      expect(failure.stack).toContain('Error 2: Error: Inner error 2');
+    });
+  });
+});