add comment and add assert to test to verify correct methods included.

Author: zhumin8

gapic-generator-java/src/test/java/com/google/api/generator/gapic/protoparser/ParserTest.java

@@ -760,6 +760,9 @@ void selectiveGenerationTest_shouldGenerateOnlySelectiveMethods() {
     assertEquals(1, services.size());
     assertEquals("EchoServiceShouldGeneratePartial", services.get(0).overriddenName());
     assertEquals(3, services.get(0).methods().size());
+    for (Method method : services.get(0).methods()) {
+      assertTrue(method.name().contains("ShouldInclude"));
+    }
   }
 
   @Test

gapic-generator-java/src/test/proto/selective_api_generation.proto

@@ -92,7 +92,9 @@ message Foobar {
   string info = 2;
 }
 
-// resource name used for message EchoRequestWithFoobarbaz.
+// resource name used only for message EchoRequestWithFoobarbaz.
+// should not be generated with selective generation when
+// AnExcludedMethod is not config as included.
 message Foobarbaz {
   option (google.api.resource) = {
     type: "showcase.googleapis.com/Foobarbaz"