Fix typo in documentation

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/suites/helpers.function b/tests/suites/helpers.function
index 0bf8189..ceac670 100644
--- a/tests/suites/helpers.function
+++ b/tests/suites/helpers.function
@@ -827,7 +827,7 @@
  * by an attempt to lock the mutex as well. A limitation of this framework is
  * that it cannot detect scenarios where there is exactly the same number of
  * calls to init and free but the calls don't match. A bug like this is
- * unlikely happen uniformly throughout the whole test suite though.
+ * unlikely to happen uniformly throughout the whole test suite though.
  *
  * If an error is detected, this framework will report what happened and the
  * test case will be marked as failed. Unfortunately, the error report cannot