Improve Darwin discovery test.

1) Don't fulfill the expectation we are waiting on until after we have logged
   our "Found device" bit.
2) Have "Found device" and "Removed device" bits actually log the data that we
   are adding/removing to our result list, so that if they don't match it's
   easier to tell what's going on.

src/darwin/Framework/CHIPTests/MTRCommissionableBrowserTests.m

@@ -104,6 +104,22 @@ - (void)controller:(MTRDeviceController *)controller didFindCommissionableDevice
 
     [_results addObject:snapshot];
 
+    XCTAssertLessThanOrEqual(_results.count, kExpectedDiscoveredDevicesCount);
+
+    __auto_type instanceName = device.instanceName;
+    __auto_type vendorId = device.vendorID;
+    __auto_type productId = device.productID;
+    __auto_type discriminator = device.discriminator;
+    __auto_type commissioningMode = device.commissioningMode;
+
+    XCTAssertEqual(instanceName.length, 16); // The  instance name is random, so just ensure the len is right.
+    XCTAssertEqualObjects(vendorId, @(kTestVendorId));
+    XCTAssertTrue([kTestProductIds containsObject:productId]);
+    XCTAssertTrue([kTestDiscriminators containsObject:discriminator]);
+    XCTAssertEqual(commissioningMode, YES);
+
+    NSLog(@"Found device %@", snapshot);
+
     if (_results.count == kExpectedDiscoveredDevicesCount) {
         // Do some sanity checking on our results and removedResults to make
         // sure we really only saw the relevant set of things.
@@ -123,39 +139,18 @@ - (void)controller:(MTRDeviceController *)controller didFindCommissionableDevice
             [self.expectation fulfill];
         }
     }
-
-    XCTAssertLessThanOrEqual(_results.count, kExpectedDiscoveredDevicesCount);
-
-    __auto_type instanceName = device.instanceName;
-    __auto_type vendorId = device.vendorID;
-    __auto_type productId = device.productID;
-    __auto_type discriminator = device.discriminator;
-    __auto_type commissioningMode = device.commissioningMode;
-
-    XCTAssertEqual(instanceName.length, 16); // The  instance name is random, so just ensure the len is right.
-    XCTAssertEqualObjects(vendorId, @(kTestVendorId));
-    XCTAssertTrue([kTestProductIds containsObject:productId]);
-    XCTAssertTrue([kTestDiscriminators containsObject:discriminator]);
-    XCTAssertEqual(commissioningMode, YES);
-
-    NSLog(@"Found Device (%@) with discriminator: %@ (vendor: %@, product: %@)", instanceName, discriminator, vendorId, productId);
 }
 
 - (void)controller:(MTRDeviceController *)controller didRemoveCommissionableDevice:(MTRCommissionableBrowserResult *)device
 {
-    __auto_type instanceName = device.instanceName;
-    __auto_type vendorId = device.vendorID;
-    __auto_type productId = device.productID;
-    __auto_type discriminator = device.discriminator;
-
-    NSLog(
-        @"Removed Device (%@) with discriminator: %@ (vendor: %@, product: %@)", instanceName, discriminator, vendorId, productId);
-
     __auto_type * snapshot = ResultSnapshot(device);
-    XCTAssertTrue([_results containsObject:snapshot], @"Removed device %@ is not something we found before", snapshot);
+    XCTAssertTrue([_results containsObject:snapshot], @"Removed device %@ is not something we found before: %@", snapshot, _results);
 
     [_removedResults addObject:snapshot];
     [_results removeObject:snapshot];
+
+    NSLog(@"Removed device %@", snapshot);
+
 }
 @end