[mutter] tests: Add env var to override plugin used for tests

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit c663f4ae849fa7f2a99e380d898e33c18b2c6e8b
Author: Jonas Ådahl <jadahl gmail com>
Date:   Mon Jul 16 10:49:52 2018 +0200

    tests: Add env var to override plugin used for tests
    
    This is so that the test suite can point at the non-installed version.

 src/tests/test-utils.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)
---
diff --git a/src/tests/test-utils.c b/src/tests/test-utils.c
index ebc076a52..3df98f305 100644
--- a/src/tests/test-utils.c
+++ b/src/tests/test-utils.c
@@ -447,5 +447,11 @@ test_client_destroy (TestClient *client)
 const char *
 test_get_plugin_name (void)
 {
-  return "libdefault";
+  const char *name;
+
+  name = g_getenv ("MUTTER_TEST_PLUGIN_PATH");
+  if (name)
+    return name;
+  else
+    return "libdefault";
 }