test createPlaintextS2AChannelCredentials.

Author: rmehta19

gax-java/gax-grpc/src/test/java/com/google/api/gax/grpc/InstantiatingGrpcChannelProviderTest.java

@@ -982,6 +982,20 @@ private FixedHeaderProvider getHeaderProviderWithApiKeyHeader() {
     return FixedHeaderProvider.create(header);
   }
 
+  @Test
+  void createPlaintextToS2AChannelCredentials_emptyPlaintextAddress_returnsNull() {
+    InstantiatingGrpcChannelProvider provider =
+        InstantiatingGrpcChannelProvider.newBuilder().build();
+    assertThat(provider.createPlaintextToS2AChannelCredentials("")).isNull();
+  }
+
+  @Test
+  void createPlaintextToS2AChannelCredentials_success() {
+    InstantiatingGrpcChannelProvider provider =
+        InstantiatingGrpcChannelProvider.newBuilder().build();
+    assertThat(provider.createPlaintextToS2AChannelCredentials("localhost:8080")).isNotNull();
+  }
+
   @Test
   void createMtlsToS2AChannelCredentials_missingAllFiles_throws() throws IOException {
     InstantiatingGrpcChannelProvider provider =