add missing slnx xml root node test

Author: IOBYTE

test/cli/project_test.py

@@ -139,6 +139,14 @@ def test_sln_project_file_not_found(tmpdir):
     __test_project_error(tmpdir, "sln", content, expected)
 
 
+def test_snlx_no_xml_root(tmpdir):
+    content = '<?xml version="1.0" encoding="utf-8"?>'
+
+    expected = "Visual Studio solution file has no XML root node"
+
+    __test_project_error(tmpdir, "slnx", content, expected)
+
+
 def test_vcxproj_no_xml_root(tmpdir):
     content = '<?xml version="1.0" encoding="utf-8"?>'