Add validation for primary and secondary stores

lib/gitlab/redis/multi_store.rb

@@ -40,12 +40,11 @@ module Gitlab
       ).freeze
 
       def initialize(primary_store, secondary_store, instance_name = nil)
-        raise ArgumentError, 'primary_store is required' unless primary_store
-        raise ArgumentError, 'secondary_store is required' unless secondary_store
-
         @primary_store = primary_store
         @secondary_store = secondary_store
         @instance_name = instance_name
+
+        validate_stores!
       end
 
       READ_COMMANDS.each do |name|
@@ -198,6 +197,13 @@ module Gitlab
         @method_missing_counter.increment(command: command_name, innamece_name: instance_name)
       end
 
+      def validate_stores!
+        raise ArgumentError, 'primary_store is required' unless primary_store
+        raise ArgumentError, 'secondary_store is required' unless secondary_store
+        raise ArgumentError, 'invalid primary_store' unless primary_store.is_a?(::Redis)
+        raise ArgumentError, 'invalid secondary_store' unless secondary_store.is_a?(::Redis)
+      end
+
       def log_error(exception, command_name, extra = {})
         Gitlab::ErrorTracking.log_exception(
           exception,

spec/lib/gitlab/redis/multi_store_spec.rb

@@ -48,6 +48,26 @@ RSpec.describe Gitlab::Redis::MultiStore do
     end
   end
 
+  context 'when primary_store is not a ::Redis instance' do
+    before do
+      allow(primary_store).to receive(:is_a?).with(::Redis).and_return(false)
+    end
+
+    it 'fails with exception' do
+      expect { described_class.new(primary_store, secondary_store, instance_name) }.to raise_error(ArgumentError, /invalid primary_store/)
+    end
+  end
+
+  context 'when secondary_store is not a ::Redis instance' do
+    before do
+      allow(secondary_store).to receive(:is_a?).with(::Redis).and_return(false)
+    end
+
+    it 'fails with exception' do
+      expect { described_class.new(primary_store, secondary_store, instance_name) }.to raise_error(ArgumentError, /invalid secondary_store/)
+    end
+  end
+
   context 'with READ redis commands' do
     let_it_be(:key1) { "redis:{1}:key_a" }
     let_it_be(:key2) { "redis:{1}:key_b" }