fix warnings in testfile

test/unittest/shellmatta_utils/test_utils_writeEcho.cpp

@@ -17,8 +17,8 @@ static shellmatta_retCode_t writeFct(const char* data, uint32_t length)
 TEST_CASE( "shellmatta_writeEcho echo enabled" ) {
 
     shellmatta_instance_t inst;
-    char buffer[20];
-    char dummyData[29];
+    char buffer[20] = {0};
+    char dummyData[29] = {0};
 
     inst.buffer = buffer;
     inst.bufferSize = 20;
@@ -42,8 +42,8 @@ TEST_CASE( "shellmatta_writeEcho echo enabled" ) {
 TEST_CASE( "shellmatta_writeEcho echo disabled" ) {
 
     shellmatta_instance_t inst;
-    char buffer[20];
-    char dummyData[29];
+    char buffer[20] = {0};
+    char dummyData[29] = {0};
 
     inst.buffer = buffer;
     inst.bufferSize = 20;