ENH: Add GoogleTest unit test ImageRegionIterator.IsConstructedAtBegin

Checks that an iterator, constructed by `IteratorType(image, region)` is at the
begin. Checks 22 different iterator types from Core/Common.

Author: N-Dekker

Modules/Core/Common/test/CMakeLists.txt

@@ -1735,6 +1735,7 @@ set(ITKCommonGTests
     itkImageIORegionGTest.cxx
     itkImageRandomConstIteratorWithIndexGTest.cxx
     itkImageRegionGTest.cxx
+    itkImageRegionIteratorGTest.cxx
     itkIndexGTest.cxx
     itkIndexRangeGTest.cxx
     itkLightObjectGTest.cxx

Modules/Core/Common/test/itkImageRegionIteratorGTest.cxx

@@ -0,0 +1,136 @@
+/*=========================================================================
+ *
+ *  Copyright NumFOCUS
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *         https://www.apache.org/licenses/LICENSE-2.0.txt
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *=========================================================================*/
+
+// First include the header files to be tested:
+#include "itkImageConstIterator.h"
+#include "itkImageConstIteratorWithIndex.h"
+#include "itkImageConstIteratorWithOnlyIndex.h"
+#include "itkImageIterator.h"
+#include "itkImageIteratorWithIndex.h"
+#include "itkImageLinearConstIteratorWithIndex.h"
+#include "itkImageLinearIteratorWithIndex.h"
+#include "itkImageRegionConstIterator.h"
+#include "itkImageRegionConstIteratorWithIndex.h"
+#include "itkImageRegionConstIteratorWithOnlyIndex.h"
+#include "itkImageRegionExclusionConstIteratorWithIndex.h"
+#include "itkImageRegionExclusionIteratorWithIndex.h"
+#include "itkImageRegionIterator.h"
+#include "itkImageRegionIteratorWithIndex.h"
+#include "itkImageRegionReverseConstIterator.h"
+#include "itkImageRegionReverseIterator.h"
+#include "itkImageReverseConstIterator.h"
+#include "itkImageReverseIterator.h"
+#include "itkImageScanlineConstIterator.h"
+#include "itkImageScanlineIterator.h"
+#include "itkImageSliceConstIteratorWithIndex.h"
+#include "itkImageSliceIteratorWithIndex.h"
+
+#include "itkImage.h"
+#include <gtest/gtest.h>
+#include <type_traits> // For false_type and true_type.
+
+namespace
+{
+// Has_IsAtBegin tells whether the specified iterator type has an `IsAtBegin()` member function, returning a `bool`. It
+// is inspired by "How to detect whether there is a specific member variable in class?", answered by Andy Prowl, Jan 25,
+// 2013 at https://stackoverflow.com/a/14523787 (the `has_id` example).
+template <typename TIterator, typename = bool>
+struct Has_IsAtBegin : std::false_type
+{};
+
+template <typename TIterator>
+struct Has_IsAtBegin<TIterator, decltype(std::declval<TIterator>().IsAtBegin())> : std::true_type
+{};
+
+
+template <typename TIterator>
+void
+CheckConstructedAtBegin()
+{
+  using ImageType = typename TIterator::ImageType;
+  using IndexType = typename TIterator::IndexType;
+  using SizeType = typename TIterator::SizeType;
+  using RegionType = typename TIterator::RegionType;
+
+  const auto image = ImageType::New();
+
+  // Use a small image size, so that the unit test won't take a long time.
+  static constexpr itk::SizeValueType imageSizeValue{ 4 };
+
+  image->SetRegions(SizeType::Filled(imageSizeValue));
+  image->Allocate();
+
+  // Check various regions, specified by the following `indexValue` and `sizeValue` combinations:
+  for (const itk::IndexValueType indexValue : { 0, 1 })
+  {
+    for (const auto sizeValue : { itk::SizeValueType{ 1 }, imageSizeValue - 1 })
+    {
+      const RegionType imageRegion(IndexType::Filled(indexValue), SizeType::Filled(sizeValue));
+
+      const TIterator iterator(image, imageRegion);
+      TIterator       iteratorThatGoesToBegin = iterator;
+      iteratorThatGoesToBegin.GoToBegin();
+      EXPECT_EQ(iterator, iteratorThatGoesToBegin);
+
+      if constexpr (Has_IsAtBegin<TIterator>::value)
+      {
+        // Extra check, using IsAtBegin(), if the iterator has that member function. (Some iterators
+        // do not have an IsAtBegin() member function, for example, ImageRegionConstIteratorWithIndex.)
+        EXPECT_TRUE(TIterator(image, imageRegion).IsAtBegin());
+      }
+    }
+  }
+}
+
+
+template <template <typename> typename... TIteratorTemplate>
+void
+CheckIteratorsConstructedAtBegin()
+{
+  (CheckConstructedAtBegin<TIteratorTemplate<itk::Image<int>>>(), ...);
+  (CheckConstructedAtBegin<TIteratorTemplate<itk::Image<double, 3>>>(), ...);
+}
+} // namespace
+
+
+// Checks that an iterator that is just constructed by `IteratorType(image, region)` is at the begin.
+TEST(ImageRegionIterator, IsConstructedAtBegin)
+{
+  CheckIteratorsConstructedAtBegin<itk::ImageConstIterator,
+                                   itk::ImageConstIteratorWithIndex,
+                                   itk::ImageConstIteratorWithOnlyIndex,
+                                   itk::ImageIterator,
+                                   itk::ImageIteratorWithIndex,
+                                   itk::ImageLinearConstIteratorWithIndex,
+                                   itk::ImageLinearIteratorWithIndex,
+                                   itk::ImageRegionConstIterator,
+                                   itk::ImageRegionConstIteratorWithIndex,
+                                   itk::ImageRegionConstIteratorWithOnlyIndex,
+                                   itk::ImageRegionExclusionConstIteratorWithIndex,
+                                   itk::ImageRegionExclusionIteratorWithIndex,
+                                   itk::ImageRegionIterator,
+                                   itk::ImageRegionIteratorWithIndex,
+                                   itk::ImageRegionReverseConstIterator,
+                                   itk::ImageRegionReverseIterator,
+                                   itk::ImageReverseConstIterator,
+                                   itk::ImageReverseIterator,
+                                   itk::ImageScanlineConstIterator,
+                                   itk::ImageScanlineIterator,
+                                   itk::ImageSliceConstIteratorWithIndex,
+                                   itk::ImageSliceIteratorWithIndex>();
+}