gRPC Testing Interview Questions

gRPC is a binary, contract-first framework over HTTP/2 using Protocol Buffers, so you cannot just curl JSON endpoints. You test against the proto contract, use gRPC-aware tools (grpcurl, Ghz, BloomRPC, Postman), handle four call types including streaming, and check gRPC status codes, deadlines, and schema compatibility, rather than REST verbs and JSON bodies.

Unary (single request, single response), server streaming (single request, stream of responses), client streaming (stream of requests, single response), and bidirectional streaming (both stream). Streaming calls require test approaches that handle ongoing message flows, not just one request/response.

grpcurl for manual command-line calls, Ghz for load testing, BloomRPC or Postman for interactive exploration, and language-native testing frameworks with generated stubs for automated tests. Contract testing leverages the proto definitions directly.

Use the generated client stubs to drive the stream from test code: for server streaming, collect messages into a list and assert on count, order, and content; for client streaming, send a scripted sequence and assert on the final response; for bidirectional, script both sides and assert on the interleaving. Always test the unhappy paths too: mid-stream errors, a slow consumer, deadline expiry during the stream, and clean half-close behavior, because that is where streaming bugs live.

Ghz is the standard tool: it speaks native gRPC, takes your proto (or uses server reflection), and lets you control concurrency, connection count, and request payloads while reporting latency percentiles and per-status-code counts. Keep an eye on connection reuse, since HTTP/2 multiplexes many calls over one connection, a load test with a single connection can bottleneck on flow control rather than the service. k6 with its gRPC module is a common alternative when you want load scenarios in code.

Safe changes: adding new fields with fresh field numbers, adding new RPC methods, and renaming fields (the wire format only uses numbers). Breaking changes: reusing or changing a field number, changing a field's type, removing a field without reserving its number, and changing an RPC's request or response message. Tools like buf breaking run this check in CI so an incompatible proto never reaches consumers.

Yes. The AI interviewer asks Protocol Buffers, streaming, and contract-testing questions with follow-ups and scores you across four dimensions.