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title Mock gRPC client in tests
author jamesnk
description Learn how to mock gRPC client in .NET tests.
monikerRange >= aspnetcore-3.1
ms.author wpickett
ms.custom mvc
ms.date 05/02/2022
uid grpc/test-client

Mock gRPC client in tests

[!INCLUDE]

By: James Newton-King

Testing is an important aspect of building stable and maintainable software. Part of writing high-quality tests is removing external dependencies. This article discusses using mock gRPC clients in tests to remove gRPC calls to external servers.

Example testable client app

To demonstrate client app tests, review the following type in the sample app.

View or download sample code (how to download)

The Worker is a BackgroundService that makes calls to a gRPC server.

[!code-csharp]

The preceding type:

  • Follows the Explicit Dependencies Principle.
  • TesterClient is generated automatically by the tooling package Grpc.Tools based on the test.proto file, during the build process.
  • Expects dependency injection (DI) to provide instances of TesterClient and IGreetRepository. The app is configured to use the gRPC client factory to create TesterClient.
  • Can be tested with a mocked IGreetRepository service and TesterClient client using a mock object framework, such as Moq. A mocked object is a fabricated object with a predetermined set of property and method behaviors used for testing. For more information, see xref:test/integration-tests#introduction-to-integration-tests.

For more information on the C# assets automatically generated by Grpc.Tools, see gRPC services with C#: Generated C# assets.

Mock a gRPC client

gRPC clients are concrete client types that are generated from .proto files. The concrete gRPC client has methods that translate to the gRPC service in the .proto file. For example, a service called Greeter generates a GreeterClient type with methods to call the service.

A mocking framework can mock a gRPC client type. When a mocked client is passed to the type, the test uses the mocked method instead of sending a gRPC call to a server.

[!code-csharp]

The preceding unit test:

  • Mocks IGreetRepository and TesterClient using Moq.
  • Starts the worker.
  • Verifies SaveGreeting is called with the greeting message returned by the mocked TesterClient.
  • Uses the CallHelpers from the gRPC examples

Additional resources

  • xref:grpc/test-tools
  • xref:grpc/test-services