docs: add fuzz testing design document.

site/content/en/contributions/design/fuzzing.md

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+---
+title: "Fuzzing "
+---
+
+## Overview
+
+This design document introduces **Fuzz Testing** in Envoy Gateway.
+Its goal is to detect unexpected crashes, memory leaks, and undefined behaviors in the translation of Gateway 
+API resources and configuration parsing, areas that may not be fully covered by unit tests. 
+
+Additionally, [OSS-Fuzz](https://github.com/google/oss-fuzz) 
+provides a continuous fuzzing infrastructure for popular open-source projects. By writing fuzz tests, 
+we can leverage OSS-Fuzz to continuously fuzz Envoy Gateway against a wide range of inputs, 
+improving its resilience and reliability.
+
+**Note:** This work is sponsored by the 
+[Linux Foundation Mentorship](https://mentorship.lfx.linuxfoundation.org/project/44020e81-1218-49aa-95e0-ee3e03998eb3) 
+program.
+
+## Goals
+
+* Identify fuzz targets considering the tradeoff between realism, efficiency, and maintenance effort.
+* Develop a set of initial fuzzers.
+* Integrate with OSS-Fuzz for continuous, automated fuzz testing.
+* Iteratively refine, update, and enhance fuzzers based on findings and evolving requirements.
+
+
+## Non Goals
+
+* Introducing new features to Envoy Gateway.
+* Achieving 100% code coverage.
+
+## Implementation
+
+As the fuzzers will be integrated with OSS-Fuzz, the implementation will follow best practices 
+outlined in [OSS-Fuzz Ideal Integration](https://google.github.io/oss-fuzz/advanced-topics/ideal-integration/) page.
+Fuzzers will be developed native Go fuzzing library [go-fuzz](https://go.dev/blog/fuzz-beta).
+
+### Example
+Here is an example of a simple fuzzer that tests the translation of Gateway API resource to Intermediate 
+representation (IR).
+
+```go
+func FuzzGatewayAPIToIRWithGatewayClass(f *testing.F) {
+	f.Add("valid-name", "valid-namespace", "gateway.envoyproxy.io/gatewayclass-controller")
+	f.Fuzz(func(t *testing.T, name, namespace, controllerName string) {
+		resources := &resource.Resources{
+			GatewayClass: &gwapiv1.GatewayClass{
+				ObjectMeta: metav1.ObjectMeta{
+					Name:      name,
+					Namespace: namespace,
+				},
+				Spec: gwapiv1.GatewayClassSpec{
+					ControllerName: gwapiv1.GatewayController(controllerName),
+				},
+			},
+		}
+
+		result, err := translateGatewayAPIToIR(resources)
+		require.NoError(t, err, "Error should be nil")
+		require.NotNil(t, result, "Result should not be nil")
+		require.NotNil(t, result.Resources, "Resources should not be nil")
+		require.NotNil(t, result.XdsIR, "XdsIR should not be nil")
+		require.NotNil(t, result.InfraIR, "InfraIR should not be nil")
+	})
+}
+```
+
+## Design Decisions
+* Fuzzing library: [go-fuzz](https://go.dev/blog/fuzz-beta).
+* Fuzzers directory: Fuzzers will be stored in the `test/fuzz` directory.
+
+## Conclusion
+
+Fuzz testing is an ongoing process. Once the initial fuzzers are developed, 
+crashes reported by OSS-Fuzz will be continuously monitored, and the fuzzers will be iteratively refined.
+Additionally, future efforts will be directed toward exploring the integration of fuzz testing into the CI pipeline using GitHub Actions.