fix: use separate value generator in test generation (#3294)

Sometimes a library has two requests methods with a field of the same name but different types. The TestValueGenerator keys on the short name of fields, and reuses a generated value if it has generated a value for this key (short field name). Therefore in such cases it may try to assign a string literal to a integer type.

Change to create a different TestValueGenerator for every single test case generation to avoid such cases.

src/main/java/com/google/api/codegen/transformer/TestCaseTransformer.java

@@ -64,15 +64,15 @@
 /** TestCaseTransformer contains helper methods useful for creating test views. */
 public class TestCaseTransformer {
   private final InitCodeTransformer initCodeTransformer = new InitCodeTransformer(false);
-  private final TestValueGenerator valueGenerator;
+  private final ValueProducer valueProducer;
   private boolean packageHasMultipleServices;
 
   public TestCaseTransformer(ValueProducer valueProducer) {
     this(valueProducer, false);
   }
 
   public TestCaseTransformer(ValueProducer valueProducer, boolean packageHasMultipleServices) {
-    this.valueGenerator = new TestValueGenerator(valueProducer);
+    this.valueProducer = valueProducer;
     this.packageHasMultipleServices = packageHasMultipleServices;
   }
 
@@ -355,7 +355,7 @@ private InitCodeContext createResponseInitCodeContext(
         .initValueConfigMap(ImmutableMap.of())
         .initFields(responseInitFields(outputType.getFields()))
         .fieldConfigMap(context.getProductConfig().getDefaultResourceNameFieldConfigMap())
-        .valueGenerator(valueGenerator)
+        .valueGenerator(new TestValueGenerator(valueProducer))
         .additionalInitCodeNodes(createMockResponseAdditionalSubTrees(context))
         .build();
   }