Tests: moved data to tests/data

Author: PierreRaybaut

plotpy/images/my_plot_manager.svg doc/images/my_plot_manager.svgplotpy/images/my_plot_manager.svg renamed to doc/images/my_plot_manager.svg

@@ -8,8 +8,19 @@
 ===================
 """
 
+import os.path as osp
 
-def run():
+from guidata.configtools import get_module_data_path
+
+TESTDATAPATH = get_module_data_path("plotpy", osp.join("tests", "data"))
+
+
+def get_path(filename: str) -> str:
+    """Return absolute path of test file"""
+    return osp.join(TESTDATAPATH, filename)
+
+
+def run() -> None:
     """Run plotpy test launcher"""
     from guidata.guitest import run_testlauncher