Clarify absolute path test extraction roots

tar/test/test_option_P_upper.c

@@ -59,7 +59,10 @@ DEFINE_TEST(test_extract_tar_absolute_paths)
 	UNLINK(temp_absolute_file_name);
 
 	// Extracting the archive without -P / --absolute-paths should strip leading drive letter or slash
-	r = systemf("%s -xf test.tar 2>test.err", testprog);
+	// inside its own extraction directory.
+	assertMakeDir("without-P", 0755);
+	assertChdir("without-P");
+	r = systemf("%s -xf ../test.tar 2>test.err", testprog);
 	assertEqualInt(r, 0);
 	assertFileNotExists(temp_absolute_file_name);
 
@@ -70,8 +73,9 @@ DEFINE_TEST(test_extract_tar_absolute_paths)
 	assertFileExists(temp_absolute_file_name + 1); // Skip the slash.
 #endif
 
-	// Extracting the archive with -P / --absolute-paths in a new directory should
+	// Extracting the archive with -P / --absolute-paths in a separate directory should
 	// create the file without creating a mangled path.
+	assertChdir("..");
 	assertMakeDir("with-P", 0755);
 	assertChdir("with-P");
 	r = systemf("%s --absolute-paths -xf ../test.tar", testprog);