test: Add a test that confirms errors are properly passed through for getInstance calls (#1606)

## Description

This test confirms that errors will bubble up to the user for getInstances calls which allows us to close b/388499540 as not reproducible.

## Impact

Just adding a test to confirm correct client library behaviour

## Additional Information

Two files were edited:
-  One is the test file where we added the new test
-  The other is the file that defines mock services where we needed to add a mock service for the admin client

Author: danieljbruce

src/util/mock-servers/service-implementations/bigtable-client-mock-service.ts

@@ -36,3 +36,10 @@ export class BigtableClientMockService extends MockService {
     // @ts-ignore
     proto.google.bigtable.v2.Bigtable.service;
 }
+
+export class BigtableAdminClientMockService extends MockService {
+  service =
+    // eslint-disable-next-line @typescript-eslint/ban-ts-comment
+    // @ts-ignore
+    proto.google.bigtable.admin.v2.BigtableInstanceAdmin.service;
+}

test/errors.ts

@@ -22,7 +22,10 @@ import * as assert from 'assert';
 
 import {GoogleError, grpc, ServiceError} from 'google-gax';
 import {MockServer} from '../src/util/mock-servers/mock-server';
-import {BigtableClientMockService} from '../src/util/mock-servers/service-implementations/bigtable-client-mock-service';
+import {
+  BigtableAdminClientMockService,
+  BigtableClientMockService,
+} from '../src/util/mock-servers/service-implementations/bigtable-client-mock-service';
 import {MockService} from '../src/util/mock-servers/mock-service';
 
 function isServiceError(error: any): error is ServiceError {
@@ -147,3 +150,52 @@ describe('Bigtable/Errors', () => {
     server.shutdown(() => {});
   });
 });
+
+describe('BigtableAdminClient/Errors', () => {
+  let server: MockServer;
+  let bigtable: Bigtable;
+  let service: MockService;
+
+  before(async () => {
+    // make sure we have everything initialized before starting tests
+    const port = await new Promise<string>(resolve => {
+      server = new MockServer(resolve);
+    });
+    bigtable = new Bigtable({
+      apiEndpoint: `localhost:${port}`,
+    });
+    service = new BigtableAdminClientMockService(server);
+  });
+
+  describe('with getInstances', () => {
+    const emitGetInstancesError = (stream: any) => {
+      const metadata = new grpc.Metadata();
+      stream.emit('error', {
+        code: 5,
+        details: 'getInstances error details',
+        metadata,
+      });
+    };
+    before(async () => {
+      service.setService({
+        listInstances: emitGetInstancesError,
+      });
+    });
+    it('should produce human readable error when passing through gax', async () => {
+      try {
+        await bigtable.getInstances();
+        assert.fail(
+          'An error should have been thrown by the getInstances call',
+        );
+      } catch (err) {
+        assert.strictEqual(
+          (err as ServiceError).message,
+          '5 NOT_FOUND: getInstances error details',
+        );
+      }
+    });
+  });
+  after(async () => {
+    server.shutdown(() => {});
+  });
+});