Add a simple unit test for wxHtmlPrintout pagination logic

Verify that the number of pages to be printed is as expected.

tests/html/htmprint.cpp

@@ -0,0 +1,82 @@
+///////////////////////////////////////////////////////////////////////////////
+// Name:        tests/html/htmprint.cpp
+// Purpose:     wxHtmlPrintout tests
+// Author:      Vadim Zeitlin
+// Created:     2018-05-22
+// Copyright:   (c) 2018 Vadim Zeitlin <vadim@wxwidgets.org>
+///////////////////////////////////////////////////////////////////////////////
+
+// ----------------------------------------------------------------------------
+// headers
+// ----------------------------------------------------------------------------
+
+#include "testprec.h"
+
+#if wxUSE_HTML
+
+#ifdef __BORLANDC__
+    #pragma hdrstop
+#endif
+
+#ifndef WX_PRECOMP
+    #include "wx/dcmemory.h"
+#endif // WX_PRECOMP
+
+#include "wx/html/htmprint.h"
+
+namespace
+{
+
+// Return the number of pages in the printout.
+int CountPages(wxHtmlPrintout& pr)
+{
+    REQUIRE_NOTHROW( pr.OnPreparePrinting() );
+
+    int pageMin = -1,
+        pageMax = -1,
+        selFrom = -1,
+        selTo   = -1;
+    REQUIRE_NOTHROW( pr.GetPageInfo(&pageMin, &pageMax, &selFrom, &selTo) );
+
+    // This should be always the case.
+    CHECK( pageMin == 1 );
+
+    // Return the really interesting value to the caller.
+    return pageMax;
+}
+
+} // anonymous namespace
+
+TEST_CASE("wxHtmlPrintout::Pagination", "[html][print]")
+{
+    wxHtmlPrintout pr;
+
+    wxBitmap bmp(1000, 1000);
+    wxMemoryDC dc(bmp);
+    pr.SetUp(dc);
+
+    // Empty or short HTML documents should be printed on a single page only.
+    CHECK( CountPages(pr) == 1 );
+
+    pr.SetHtmlText("<p>Hello world!</p>");
+    CHECK( CountPages(pr) == 1 );
+
+    // This one should be too big to fit on a single page.
+    pr.SetHtmlText
+       (
+            "<img width=\"100\" height=\"600\" src=\"dummy\"/>"
+            "<br/>"
+            "<img width=\"100\" height=\"600\" src=\"dummy\"/>"
+       );
+    CHECK( CountPages(pr) == 2 );
+
+    // Special case: normally images are not split, but if the image height is
+    // greater than the page height, it should be.
+    pr.SetHtmlText
+       (
+            "<img width=\"100\" height=\"2500\" src=\"dummy\"/>"
+       );
+    CHECK( CountPages(pr) == 3 );
+}
+
+#endif //wxUSE_HTML