tests CHANGE use prefix on test's sourco files

To distinguish original and test source files in debugger, use test_
prefix for test source files.
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index ee34289..b2d9894 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -21,7 +21,7 @@
     message(STATUS ${test_name})
     string(REGEX REPLACE "[a-z]*_(.*)" "\\1" name "${test_name}")
     string(REGEX REPLACE "([a-z]*)_.*" "\\1" prefix "${test_name}")
-    add_executable(${test_name} ${prefix}/${name}.c)
+    add_executable(${test_name} ${prefix}/test_${name}.c)
 endforeach(test_name)
 
 # Set common attributes of all tests