Rename test case to avoid possible name conflict

pytest does not allow two test file have same name despite they are in
different folder.

Change-Id: I568fe042f6dbe99df336d0ce4d6ed9c78305fe74
Signed-off-by: Yujun Zhang <zhang.yujunz@zte.com.cn>

diff --git a/tests/unit/collector/base_test.py b/tests/unit/collector/collector_test.py
similarity index 100%
rename from tests/unit/collector/base_test.py
rename to tests/unit/collector/collector_test.py