[gtk+] gl renderer: Add test case for last commit

[Timm Bäder <baedert src gnome org>]

commit af6adb5bc0857715c125281e2377cc0fbb157254
Author: Timm Bäder <mail baedert org>
Date:   Thu Jan 4 11:43:43 2018 +0100

    gl renderer: Add test case for last commit

 testsuite/gsk/gl/text_alpha.gl.png |  Bin 0 -> 599 bytes
 testsuite/gsk/gl/text_alpha.node   |  Bin 0 -> 188 bytes
 testsuite/gsk/meson.build          |    1 +
 3 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/testsuite/gsk/gl/text_alpha.gl.png b/testsuite/gsk/gl/text_alpha.gl.png
new file mode 100644
index 0000000..acd1d4f
Binary files /dev/null and b/testsuite/gsk/gl/text_alpha.gl.png differ
diff --git a/testsuite/gsk/gl/text_alpha.node b/testsuite/gsk/gl/text_alpha.node
new file mode 100644
index 0000000..54b236e
Binary files /dev/null and b/testsuite/gsk/gl/text_alpha.node differ
diff --git a/testsuite/gsk/meson.build b/testsuite/gsk/meson.build
index 862bbf9..7093265 100644
--- a/testsuite/gsk/meson.build
+++ b/testsuite/gsk/meson.build
@@ -42,6 +42,7 @@ gl_tests = [
   ['outset shadow blurred simple', 'outset_shadow_blurred_simple.node', 
'outset_shadow_blurred_simple.gl.png'],
   ['outset shadow blurred small', 'outset_shadow_blurred_small.node', 'outset_shadow_blurred_small.gl.png'],
   ['outset shadow blurred offset', 'outset_shadow_blurred_offset.node', 
'outset_shadow_blurred_offset.gl.png'],
+  ['Text with alpha', 'text_alpha.node', 'text_alpha.gl.png']
 ]
 
 foreach gl_test : gl_tests