Add rust_test and update TEST_MAPPING

Test: atest -c --include-subdirs external/rust/crates
Change-Id: If1c7cb1933ca92800e7433ebbff05a8f37ff67ed
diff --git a/Android.bp b/Android.bp
index ffbd99f..a43a91a 100644
--- a/Android.bp
+++ b/Android.bp
@@ -1,4 +1,4 @@
-// This file is generated by cargo2android.py --run --dependencies.
+// This file is generated by cargo2android.py --run --dependencies --tests.
 
 rust_library_host {
     name: "libprotobuf_codegen",
@@ -10,6 +10,18 @@
     ],
 }
 
+rust_test_host {
+    name: "protobuf-codegen_host_test_src_lib",
+    crate_name: "protobuf_codegen",
+    srcs: ["src/lib.rs"],
+    test_suites: ["general-tests"],
+    auto_gen_config: true,
+    edition: "2015",
+    rustlibs: [
+        "libprotobuf",
+    ],
+}
+
 rust_binary_host {
     name: "protoc-gen-rust",
     crate_name: "protoc_gen_rust",