[Security Solution][Detection Engine] Test cases for alias failure test cases where we don't copy aliases correctly (#101437)

## Summary

Test cases for signals and aliases, including a failure of where we do not copy alias data at the moment even if the target is an ECS compatible field.

For example with this mapping:

```json
{
  "dynamic": "strict",
  "properties": {
    "@timestamp": {
      "type": "date"
    },
    "host": {
      "properties": {
        "name": {
          "type": "alias",
          "path": "host_alias.name"
        }
      }
    },
    "host_alias": {
      "properties": {
        "name": {
          "type": "keyword"
        }
      }
    }
  }
}
```

If we detect this as a signal hit we should be copying over both:
* `host_alias.name` -> `host.name`
* `host_alias.name` -> `host_alias.name`

to the target signal index, but we only copy:
* `host_alias.name` -> `host_alias.name`

### Checklist

- [x] [Unit or functional tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html) were updated or added to match the most common scenarios

x-pack/test/detection_engine_api_integration/security_and_spaces/tests/aliases.ts

@@ -0,0 +1,65 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+import expect from '@kbn/expect';
+
+import { FtrProviderContext } from '../../common/ftr_provider_context';
+import {
+  createRule,
+  createSignalsIndex,
+  deleteAllAlerts,
+  deleteSignalsIndex,
+  getRuleForSignalTesting,
+  getSignalsById,
+  waitForRuleSuccessOrStatus,
+  waitForSignalsToBePresent,
+} from '../../utils';
+
+// eslint-disable-next-line import/no-default-export
+export default ({ getService }: FtrProviderContext) => {
+  const supertest = getService('supertest');
+  const esArchiver = getService('esArchiver');
+  interface HostAlias {
+    name: string;
+  }
+
+  describe('Tests involving aliases of source indexes and the signals index', () => {
+    beforeEach(async () => {
+      await createSignalsIndex(supertest);
+      await esArchiver.load('security_solution/alias');
+    });
+
+    afterEach(async () => {
+      await deleteSignalsIndex(supertest);
+      await deleteAllAlerts(supertest);
+      await esArchiver.unload('security_solution/alias');
+    });
+
+    it('Should keep the original alias value such as "host_alias" from a source index when the value is indexed', async () => {
+      const rule = getRuleForSignalTesting(['alias']);
+      const { id } = await createRule(supertest, rule);
+      await waitForRuleSuccessOrStatus(supertest, id);
+      await waitForSignalsToBePresent(supertest, 4, [id]);
+      const signalsOpen = await getSignalsById(supertest, id);
+      const hits = signalsOpen.hits.hits.map(
+        (signal) => (signal._source.host_alias as HostAlias).name
+      );
+      expect(hits).to.eql(['host name 1', 'host name 2', 'host name 3', 'host name 4']);
+    });
+
+    // TODO: Make aliases work to where we can have ECS fields such as host.name filled out
+    it.skip('Should copy alias data from a source index into the signals index in the same position when the target is ECS compatible', async () => {
+      const rule = getRuleForSignalTesting(['alias']);
+      const { id } = await createRule(supertest, rule);
+      await waitForRuleSuccessOrStatus(supertest, id);
+      await waitForSignalsToBePresent(supertest, 4, [id]);
+      const signalsOpen = await getSignalsById(supertest, id);
+      const hits = signalsOpen.hits.hits.map((signal) => (signal._source.host as HostAlias).name);
+      expect(hits).to.eql(['host name 1', 'host name 2', 'host name 3', 'host name 4']);
+    });
+  });
+};

x-pack/test/detection_engine_api_integration/security_and_spaces/tests/index.ts

@@ -13,6 +13,7 @@ export default ({ loadTestFile }: FtrProviderContext): void => {
     describe('', function () {
       this.tags('ciGroup11');
 
+      loadTestFile(require.resolve('./aliases'));
       loadTestFile(require.resolve('./add_actions'));
       loadTestFile(require.resolve('./update_actions'));
       loadTestFile(require.resolve('./add_prepackaged_rules'));

x-pack/test/functional/es_archives/security_solution/alias/data.json

@@ -0,0 +1,59 @@
+{
+  "type": "doc",
+  "value": {
+    "id": "1",
+    "index": "alias",
+    "source": {
+      "@timestamp": "2020-10-28T05:00:53.000Z",
+      "host_alias": {
+        "name": "host name 1"
+      }
+    },
+    "type": "_doc"
+  }
+}
+
+{
+  "type": "doc",
+  "value": {
+    "id": "2",
+    "index": "alias",
+    "source": {
+      "@timestamp": "2020-10-28T05:01:53.000Z",
+      "host_alias": {
+        "name": "host name 2"
+      }
+    },
+    "type": "_doc"
+  }
+}
+
+{
+  "type": "doc",
+  "value": {
+    "id": "3",
+    "index": "alias",
+    "source": {
+      "@timestamp": "2020-10-28T05:02:53.000Z",
+      "host_alias": {
+        "name": "host name 3"
+      }
+    },
+    "type": "_doc"
+  }
+}
+
+{
+  "type": "doc",
+  "value": {
+    "id": "4",
+    "index": "alias",
+    "source": {
+      "@timestamp": "2020-10-28T05:03:53.000Z",
+      "host_alias": {
+        "name": "host name 4"
+      }
+    },
+    "type": "_doc"
+  }
+}

x-pack/test/functional/es_archives/security_solution/alias/mappings.json

@@ -0,0 +1,36 @@
+{
+  "type": "index",
+  "value": {
+    "index": "host_alias",
+    "mappings": {
+      "dynamic": "strict",
+      "properties": {
+        "@timestamp": {
+          "type": "date"
+        },
+        "host": {
+          "properties": {
+            "name": {
+              "type": "alias",
+              "path": "host_alias.name"
+            }
+          }
+        },
+        "host_alias": {
+          "properties": {
+            "name": {
+              "type": "keyword"
+            }
+          }
+        }
+      }
+    },
+    "settings": {
+      "index": {
+        "refresh_interval": "1s",
+        "number_of_replicas": "1",
+        "number_of_shards": "1"
+      }
+    }
+  }
+}