[ci] fix macos test error, add command for unit-test

Author: fangq

README.md

@@ -77,6 +77,17 @@ including Windows, Linux, and macOS.
 5. You can install the locally built package using:
    `python3 -m pip install --force-reinstall iso2mesh-*.whl`
 
+### Run built-in unit-tests
+
+If you want to modify the source, and verify that it still produces correct results, you can run
+the built-in unit-test script inside the downloaded git repository by using this command
+inside the `pyiso2mesh` root folder
+
+```bash
+   python -m unittest test.run_test
+```
+
+
 ## How to Use
 
 `pyiso2mesh` inherits the "trademark" **one-liner mesh generator** style from its MATLAB/Octave counterpart

test/run_test.py

@@ -699,7 +699,7 @@ def test_cgalv2m(self):
             "cgalmesh",
         )
         self.assertEqual(removedupelem(fc[:, :3]).shape[0], 0)
-        self.assertAlmostEqual(sum(elemvolume(no[:, :3], el[:, :4])), 0.7455, 4)
+        self.assertAlmostEqual(sum(elemvolume(no[:, :3], el[:, :4])), 0.7455, 3)
 
 
 if __name__ == "__main__":