Rust: Add Testing cross-content entry (#5608)

* Rust: Add Testing cross-content entry.

.doc_gen/metadata/cross_metadata.yaml

@@ -707,4 +707,24 @@ cross_FMPlayground:
   service_main: bedrock-runtime
   services:
     bedrock-runtime:
-
+cross_Testing:
+  title: Example approaches for unit and integration testing with an &AWS; SDK
+  title_abbrev: Unit and integration test with an SDK
+  synopsis: examples for best-practice techniques when writing unit and integration tests using an &AWS; SDK.
+  languages:
+    Rust:
+      versions:
+        - sdk_version: 1
+          github: rust_dev_preview/examples/testing
+          excerpts:
+            - description: Cargo.toml for testing examples.
+              snippet_files:
+                - rust_dev_preview/examples/testing/Cargo.toml
+            - description: Unit testing example using automock and a service wrapper.
+              snippet_files:
+                - rust_dev_preview/examples/testing/src/wrapper.rs
+            - description: Integration testing example using StaticReplayClient.
+              snippet_files:
+                - rust_dev_preview/examples/testing/src/replay.rs
+  services:
+    s3: