gRPC Mocking and Testing

🗓️ Last updated on February 23, 2022 | 5 | Improve this page



In gRPC, a client application can directly call a method on a server application on a different machine as if it were a local object, making it easier for you to create distributed applications and services. As in many RPC systems, gRPC is based around the idea of defining a service, specifying the methods that can be called remotely with their parameters and return types. So that’s a perfect fit for Microcks Service | API model and features 😉

Starting with version 1.3.0, Microcks is supporting gRPC mocking and testing thanks to the new multi-artifacts support feature. In order to use gRPC in Microcks, you will need 2 artifacts for each Service definition:

  • A gRPC / Protocol Buffers file definition that holds the Service metadata and operations definitions,
  • A Postman Collection file that holds the mock examples (requests and responses) for the different operations of the gRPC Service.


In order to be correctly imported and understood by Microcks, your gRPC and Postman files should follow a little set of reasonable conventions and best practices.

  • As of today Microcks only supports proto3 syntax as it is now the default and encouraged version from gRPC community,

  • gRPC doesn’t have the notion of Service version. In Microcks, this notion is critical and we will use the package information in Protofile to compute a version.

    • For package name containing containing more than 2 paths levels, we’ll extract the last one as being the version. So package io.github.microcks.grpc.hello.v1; will produce version v1
    • We’ll keep unchanged simplest package named, so package com.acme; will produce version com.acme that is not very unique 😞.
    • So be sure to follow gRPC versioning best practices !
  • Your Postman collection description will need to have a name that matches the gRPC service name and a custom property version that matches the above computed version,

  • Your Postman collection will need to organize examples into requests having the same name and url as the gRPC methods,

  • Your Postman collection will hold examples defined in JSON as JSON is a textual format easier to use than binary Protobuf 😅

We recommend having a look at our sample gRPC for HelloService as well as the companion Postman collection to fully understand and see those conventions in action.


Let’s dive in details of our sample HelloService gRPC service.

Specifying Service structure

This is a fairly trivial gRPC Service that just greet new comers. You can see below the definition found in hello-v1.proto .

syntax = "proto3";

package io.github.microcks.grpc.hello.v1;

option java_multiple_files = true;

message HelloRequest {
    string firstname = 1;
    string lastname = 2;

message HelloResponse {
    string greeting = 1;

service HelloService {
    rpc greeting(HelloRequest) returns (HelloResponse);

Considering the package of this proto file, when imported into Microcks, it will discover the HelloService with version v1 and the unique operation greeting.

Specifying Service examples

Specification of examples is done using a Postman Collection as examples cannot be attached to main Profofile and thanks to Microcks 1.3.0 multi-artifacts support feature.

Using Postman, just create a new Collection - using the same name as gRPC Service and adding the custom property version at the beginning of description like illustrated below:


You can now start organizing and creating requests that are matching with the gRPC service method name. For our example, we’re specifying the greeting request for the greeting gRPC method.


The next step is now to create a bunch of examples for each of the requests/operations of your Collection as explained by the Postman documentation . You’ll give each example a meaningful name regarding the use-case it is supposed to represent. Example url should also match with the name of the gRPC method; here we have a simple http:///greeting.

As JSON / Protobuf translation is bi-directional, you’ll define examples using simple JSON for request body and for response body as well. Below is a basic example but Templating expressions and functions are obviously supported:


Finally, when you have defined all examples and optional test scripts on your requests, you should export your Collection as a JSON file using the Collection v2 format like shown below. Just put the result JSON file into your favorite Source Configuration Management tool for an easy integration with Microcks.

Importing artifacts

Both artifacts should be imported into Microcks either through direct upload or scheduled import . The important thing to notice is that the gRPC Protofile artifact represents the main or primary artifact for this service definition and that the Postman Collection represents a secondary artifact. You have to mention it when importing it otherwise your gRPC definition will be overwritten!

Defining dispatch rules

The final step for assembling data coming from gRPC Protofile and Postman Collection is to define how to dispatch requests. As explained into Using exposed mocks , Microcks is using Dispatcher and Dispatching Rules for finding an appropriate response to return when receiving a mock request. For gRPC, we can typically use a JSON_BODY dispatcher as explained into Custom dispatching rules .

Starting with Microcks 1.4.0, you’ll be able to directly import these dispatching rules from your Git repository as well, thanks to API Metadata documents!

Before Microcks 1.4.0 you should use the Microcks web console to edit the greeting operation properties and change the dispatcher and its rules as shown below. Here-after we have defined a simple rule that is routing incoming requests depending on the value of the firstname property of the incoming message.


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