build: use python f-strings

Change-Id: I5a6537d263d8bd6297b0975f34c90dd76b9468cd
diff --git a/tests/wscript b/tests/wscript
index 3ecb2e0..5a21139 100644
--- a/tests/wscript
+++ b/tests/wscript
@@ -3,8 +3,8 @@
 
 def build(bld):
     bld.program(
-        target='../unit-tests',
+        target=f'{top}/unit-tests',
         name='unit-tests',
-        source=bld.path.ant_glob(['*.cpp'] + ['%s/**/*.cpp' % tool for tool in bld.env.BUILD_TOOLS]),
-        use=['core-objects'] + ['%s-objects' % tool for tool in bld.env.BUILD_TOOLS],
+        source=bld.path.ant_glob(['*.cpp'] + [f'{tool}/**/*.cpp' for tool in bld.env.BUILD_TOOLS]),
+        use=['core-objects'] + [f'{tool}-objects' for tool in bld.env.BUILD_TOOLS],
         install_path=None)