[ci] Fix pdf thumbnail unit tests flakiness (#13248)

* [ci] reduce pdf preview and thumbnail flakiness

* [ci] run pdf thumbnail tests

* [meta] add pdf modules to new issue template

.github/ISSUE_TEMPLATE/bug_report.yml

@@ -39,6 +39,8 @@ body:
       - Image Resizer
       - Keyboard Manager
       - MD Preview
+      - PDF Preview
+      - PDF Thumbnail
       - PowerRename
       - PowerToys Run
       - Shortcut Guide

.pipelines/ci/templates/build-powertoys-steps.yml

@@ -121,6 +121,7 @@ steps:
     testSelector: 'testAssemblies'
     testAssemblyVer2: |
       **\UnitTests-SvgThumbnailProvider.dll
+      **\UnitTests-PdfThumbnailProvider.dll
       **\Microsoft.PowerToys.Settings.UI.UnitTests.dll
       **\UnitTests-MarkdownPreviewHandler.dll
       **\UnitTests-PdfPreviewHandler.dll

src/modules/previewpane/UnitTests-PdfPreviewHandler/PdfPreviewHandlerTest.cs

@@ -66,16 +66,18 @@ namespace PdfPreviewHandlerUnitTests
         private static IStream GetMockStream(byte[] sourceArray)
         {
             var streamMock = new Mock<IStream>();
-            var firstCall = true;
+            int bytesRead = 0;
+
             streamMock
                 .Setup(x => x.Read(It.IsAny<byte[]>(), It.IsAny<int>(), It.IsAny<IntPtr>()))
                 .Callback<byte[], int, IntPtr>((buffer, countToRead, bytesReadPtr) =>
                 {
-                    if (firstCall)
+                    int actualCountToRead = Math.Min(sourceArray.Length - bytesRead, countToRead);
+                    if (actualCountToRead > 0)
                     {
-                        Array.Copy(sourceArray, 0, buffer, 0, sourceArray.Length);
+                        Array.Copy(sourceArray, bytesRead, buffer, 0, actualCountToRead);
-                        Marshal.WriteInt32(bytesReadPtr, sourceArray.Length);
+                        Marshal.WriteInt32(bytesReadPtr, actualCountToRead);
-                        firstCall = false;
+                        bytesRead += actualCountToRead;
                     }
                     else
                     {

src/modules/previewpane/UnitTests-PdfThumbnailProvider/PdfThumbnailProviderTests.cs

@@ -70,16 +70,18 @@ namespace PdfThumbnailProviderUnitTests
         private static IStream GetMockStream(byte[] sourceArray)
         {
             var streamMock = new Mock<IStream>();
-            var firstCall = true;
+            int bytesRead = 0;
+
             streamMock
                 .Setup(x => x.Read(It.IsAny<byte[]>(), It.IsAny<int>(), It.IsAny<IntPtr>()))
                 .Callback<byte[], int, IntPtr>((buffer, countToRead, bytesReadPtr) =>
                 {
-                    if (firstCall)
+                    int actualCountToRead = Math.Min(sourceArray.Length - bytesRead, countToRead);
+                    if (actualCountToRead > 0)
                     {
-                        Array.Copy(sourceArray, 0, buffer, 0, sourceArray.Length);
+                        Array.Copy(sourceArray, bytesRead, buffer, 0, actualCountToRead);
-                        Marshal.WriteInt32(bytesReadPtr, sourceArray.Length);
+                        Marshal.WriteInt32(bytesReadPtr, actualCountToRead);
-                        firstCall = false;
+                        bytesRead += actualCountToRead;
                     }
                     else
                     {