feat: Add a test proxy for Bigtable client conformance tests

google-cloud-bigtable/lib/google/cloud/bigtable.rb

@@ -163,6 +163,7 @@ def self.new_with_emulator project_id, emulator_host, timeout
       def self.resolve_credentials given_credentials, scope
         credentials = given_credentials || default_credentials(scope: scope)
         return credentials if credentials.is_a? Google::Auth::Credentials
+        return credentials if credentials.is_a? GRPC::Core::Channel
         Bigtable::Credentials.new credentials, scope: scope
       end
 

google-cloud-bigtable/lib/google/cloud/bigtable/mutation_operations.rb

@@ -245,7 +245,7 @@ def check_and_mutate_row key, predicate, on_match: nil, otherwise: nil
           response = service.check_and_mutate_row(
             path,
             key,
-            predicate_filter: predicate.to_grpc,
+            predicate_filter: predicate&.to_grpc,
             true_mutations:   true_mutations,
             false_mutations:  false_mutations,
             app_profile_id:   @app_profile_id

google-cloud-bigtable/test/test_proxy/Gemfile

@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+source "https://rubygems.org"
+
+gem "google-cloud-bigtable", path: "../../"
+gem "grpc", "~> 1.62"
+gem "grpc-tools", "~> 1.62"
+gem "googleapis-common-protos", "~> 1.5"
+gem "googleapis-common-protos-types", "~> 1.14"

google-cloud-bigtable/test/test_proxy/README.md

@@ -0,0 +1,28 @@
+
+This is a test proxy for Bigtable client conformance tests, created following these guides: https://github.com/googleapis/cloud-bigtable-clients-test/blob/main/docs/test_proxy.md#additional-notes
+
+## Run the Proxy
+
+Run `bundle install` and then:
+
+```bash
+$ export PORT=1234 # default 9999 if not set
+$ bundle exec ruby test_proxy.rb
+```
+
+## Protos
+
+The file `proto/test_proxy.proto` was copied from https://github.com/googleapis/cndb-client-testing-protos/blob/main/google/bigtable/testproxy/test_proxy.proto, and compiled to `lib` via:
+
+```bash
+$ git clone git@github.com:googleapis/googleapis
+$ git clone git@github.com/googleapis/cndb-client-testing-protos
+
+ $ bundle exec grpc_tools_ruby_protoc \
+ -I googleapis \
+ -I cndb-client-testing-protos \
+ --ruby_out=lib \
+ --grpc_out=lib \
+ --proto_path=proto \
+ proto/test_proxy.proto
+ ```