More explicit tests for nil behaviors on fields.

Code already works, but make a bank of tests that call it out so things are
very clean in the future just to be safe.

objectivec/Tests/GPBMessageTests+Runtime.m

@@ -326,6 +326,17 @@
 //%    [msg release];
 //%  }
 //%
+//%PDDM-DEFINE PROTO2_TEST_CLEAR_FIELD_WITH_NIL(FIELD, VALUE)
+//%  {  // optional##FIELD
+//%    Message2 *msg = [[Message2 alloc] init];
+//%    XCTAssertFalse(GPBMessageHasFieldNumberSet(msg, Message2_FieldNumber_Optional##FIELD));
+//%    msg.optional##FIELD = VALUE;
+//%    XCTAssertTrue(GPBMessageHasFieldNumberSet(msg, Message2_FieldNumber_Optional##FIELD));
+//%    msg.optional##FIELD = nil;
+//%    XCTAssertFalse(GPBMessageHasFieldNumberSet(msg, Message2_FieldNumber_Optional##FIELD));
+//%    [msg release];
+//%  }
+//%
 //%PDDM-DEFINE PROTO2_TEST_HAS_FIELDS()
 //%PROTO2_TEST_HAS_FIELD(Int32, 1, 0)
 //%PROTO2_TEST_HAS_FIELD(Int64, 1, 0)
@@ -347,6 +358,14 @@
 //%  //
 //%
 //%PROTO2_TEST_HAS_FIELD(Enum, Message2_Enum_Bar, Message2_Enum_Foo)
+//%  //
+//%  // Nil can also be used to clear strings, bytes, groups, and messages.
+//%  //
+//%
+//%PROTO2_TEST_CLEAR_FIELD_WITH_NIL(String, @"foo")
+//%PROTO2_TEST_CLEAR_FIELD_WITH_NIL(Bytes, [@"foo" dataUsingEncoding:NSUTF8StringEncoding])
+//%PROTO2_TEST_CLEAR_FIELD_WITH_NIL(Group, [Message2_OptionalGroup message])
+//%PROTO2_TEST_CLEAR_FIELD_WITH_NIL(Message, [Message2 message])
 //%PDDM-EXPAND PROTO2_TEST_HAS_FIELDS()
 // This block of code is generated, do not edit it directly.
 
@@ -658,13 +677,57 @@
     [msg release];
   }
 
+  //
+  // Nil can also be used to clear strings, bytes, groups, and messages.
+  //
+
+  {  // optionalString
+    Message2 *msg = [[Message2 alloc] init];
+    XCTAssertFalse(GPBMessageHasFieldNumberSet(msg, Message2_FieldNumber_OptionalString));
+    msg.optionalString = @"foo";
+    XCTAssertTrue(GPBMessageHasFieldNumberSet(msg, Message2_FieldNumber_OptionalString));
+    msg.optionalString = nil;
+    XCTAssertFalse(GPBMessageHasFieldNumberSet(msg, Message2_FieldNumber_OptionalString));
+    [msg release];
+  }
+
+  {  // optionalBytes
+    Message2 *msg = [[Message2 alloc] init];
+    XCTAssertFalse(GPBMessageHasFieldNumberSet(msg, Message2_FieldNumber_OptionalBytes));
+    msg.optionalBytes = [@"foo" dataUsingEncoding:NSUTF8StringEncoding];
+    XCTAssertTrue(GPBMessageHasFieldNumberSet(msg, Message2_FieldNumber_OptionalBytes));
+    msg.optionalBytes = nil;
+    XCTAssertFalse(GPBMessageHasFieldNumberSet(msg, Message2_FieldNumber_OptionalBytes));
+    [msg release];
+  }
+
+  {  // optionalGroup
+    Message2 *msg = [[Message2 alloc] init];
+    XCTAssertFalse(GPBMessageHasFieldNumberSet(msg, Message2_FieldNumber_OptionalGroup));
+    msg.optionalGroup = [Message2_OptionalGroup message];
+    XCTAssertTrue(GPBMessageHasFieldNumberSet(msg, Message2_FieldNumber_OptionalGroup));
+    msg.optionalGroup = nil;
+    XCTAssertFalse(GPBMessageHasFieldNumberSet(msg, Message2_FieldNumber_OptionalGroup));
+    [msg release];
+  }
+
+  {  // optionalMessage
+    Message2 *msg = [[Message2 alloc] init];
+    XCTAssertFalse(GPBMessageHasFieldNumberSet(msg, Message2_FieldNumber_OptionalMessage));
+    msg.optionalMessage = [Message2 message];
+    XCTAssertTrue(GPBMessageHasFieldNumberSet(msg, Message2_FieldNumber_OptionalMessage));
+    msg.optionalMessage = nil;
+    XCTAssertFalse(GPBMessageHasFieldNumberSet(msg, Message2_FieldNumber_OptionalMessage));
+    [msg release];
+  }
+
 //%PDDM-EXPAND-END PROTO2_TEST_HAS_FIELDS()
 }
 
 - (void)testProto3SingleFieldHasBehavior {
   //
-  // Setting to any value including the default value (0) should result has*
-  // being true.
+  // Setting to any value but the default value (0) should result has*
+  // being true.  When set to the default, shouldn't be true.
   //
 
 //%PDDM-DEFINE PROTO3_TEST_HAS_FIELD(FIELD, NON_ZERO_VALUE, ZERO_VALUE)
@@ -678,6 +741,17 @@
 //%    [msg release];
 //%  }
 //%
+//%PDDM-DEFINE PROTO3_TEST_CLEAR_FIELD_WITH_NIL(FIELD, VALUE)
+//%  {  // optional##FIELD
+//%    Message3 *msg = [[Message3 alloc] init];
+//%    XCTAssertFalse(GPBMessageHasFieldNumberSet(msg, Message3_FieldNumber_Optional##FIELD));
+//%    msg.optional##FIELD = VALUE;
+//%    XCTAssertTrue(GPBMessageHasFieldNumberSet(msg, Message3_FieldNumber_Optional##FIELD));
+//%    msg.optional##FIELD = nil;
+//%    XCTAssertFalse(GPBMessageHasFieldNumberSet(msg, Message3_FieldNumber_Optional##FIELD));
+//%    [msg release];
+//%  }
+//%
 //%PDDM-DEFINE PROTO3_TEST_HAS_FIELDS()
 //%PROTO3_TEST_HAS_FIELD(Int32, 1, 0)
 //%PROTO3_TEST_HAS_FIELD(Int64, 1, 0)
@@ -695,10 +769,17 @@
 //%PROTO3_TEST_HAS_FIELD(String, @"foo", @"")
 //%PROTO3_TEST_HAS_FIELD(Bytes, [@"foo" dataUsingEncoding:NSUTF8StringEncoding], [NSData data])
 //%  //
-//%  // Test doesn't apply to optionalGroup/optionalMessage.
+//%  // Test doesn't apply to optionalMessage (no groups in proto3).
 //%  //
 //%
 //%PROTO3_TEST_HAS_FIELD(Enum, Message3_Enum_Bar, Message3_Enum_Foo)
+//%  //
+//%  // Nil can also be used to clear strings, bytes, and messages (no groups in proto3).
+//%  //
+//%
+//%PROTO3_TEST_CLEAR_FIELD_WITH_NIL(String, @"foo")
+//%PROTO3_TEST_CLEAR_FIELD_WITH_NIL(Bytes, [@"foo" dataUsingEncoding:NSUTF8StringEncoding])
+//%PROTO3_TEST_CLEAR_FIELD_WITH_NIL(Message, [Message3 message])
 //%PDDM-EXPAND PROTO3_TEST_HAS_FIELDS()
 // This block of code is generated, do not edit it directly.
 
@@ -853,7 +934,7 @@
   }
 
   //
-  // Test doesn't apply to optionalGroup/optionalMessage.
+  // Test doesn't apply to optionalMessage (no groups in proto3).
   //
 
   {  // optionalEnum
@@ -866,6 +947,40 @@
     [msg release];
   }
 
+  //
+  // Nil can also be used to clear strings, bytes, and messages (no groups in proto3).
+  //
+
+  {  // optionalString
+    Message3 *msg = [[Message3 alloc] init];
+    XCTAssertFalse(GPBMessageHasFieldNumberSet(msg, Message3_FieldNumber_OptionalString));
+    msg.optionalString = @"foo";
+    XCTAssertTrue(GPBMessageHasFieldNumberSet(msg, Message3_FieldNumber_OptionalString));
+    msg.optionalString = nil;
+    XCTAssertFalse(GPBMessageHasFieldNumberSet(msg, Message3_FieldNumber_OptionalString));
+    [msg release];
+  }
+
+  {  // optionalBytes
+    Message3 *msg = [[Message3 alloc] init];
+    XCTAssertFalse(GPBMessageHasFieldNumberSet(msg, Message3_FieldNumber_OptionalBytes));
+    msg.optionalBytes = [@"foo" dataUsingEncoding:NSUTF8StringEncoding];
+    XCTAssertTrue(GPBMessageHasFieldNumberSet(msg, Message3_FieldNumber_OptionalBytes));
+    msg.optionalBytes = nil;
+    XCTAssertFalse(GPBMessageHasFieldNumberSet(msg, Message3_FieldNumber_OptionalBytes));
+    [msg release];
+  }
+
+  {  // optionalMessage
+    Message3 *msg = [[Message3 alloc] init];
+    XCTAssertFalse(GPBMessageHasFieldNumberSet(msg, Message3_FieldNumber_OptionalMessage));
+    msg.optionalMessage = [Message3 message];
+    XCTAssertTrue(GPBMessageHasFieldNumberSet(msg, Message3_FieldNumber_OptionalMessage));
+    msg.optionalMessage = nil;
+    XCTAssertFalse(GPBMessageHasFieldNumberSet(msg, Message3_FieldNumber_OptionalMessage));
+    [msg release];
+  }
+
 //%PDDM-EXPAND-END PROTO3_TEST_HAS_FIELDS()
 }