FindPNG: Create an imported PNG::PNG target (#15911)

Imported targets are now the recommended way of dealing with external
library dependencies.  Add one for FindPNG and update documentation
accordingly.  Also add a test case activated by CMake_TEST_FindPNG.

1 files changed, 20 insertions, 0 deletions

diff --git a/Tests/FindPNG/Test/main.c b/Tests/FindPNG/Test/main.c
new file mode 100644
index 0000000..27e1478
--- /dev/null
+++ b/Tests/FindPNG/Test/main.c
@@ -0,0 +1,20 @@
+#include <assert.h>
+#include <string.h>
+#include <png.h>
+
+int main()
+{
+  png_uint_32 png_version;
+  char png_version_string[16];
+
+  png_version = png_access_version_number ();
+
+  snprintf (png_version_string, 16, "%i.%i.%i",
+            png_version / 10000,
+            (png_version % 10000) / 100,
+            png_version % 100);
+
+  assert (strcmp(png_version_string, CMAKE_EXPECTED_PNG_VERSION) == 0);
+
+  return 0;
+}