[Lang] [test] Add ti.get_rel_eps() for maximal relative error toleran…

…ce on current backend (#1798)

* [test] Add default_epsilon_of_arch to make tests pass on Metal

* rename

python/taichi/testing.py

@@ -2,6 +2,18 @@
 
 
 # Helper functions
+def get_rel_eps():
+    arch = ti.cfg.arch
+    if arch == ti.opengl:
+        return 1e-3
+    elif arch == ti.metal:
+        # Debatable, different hardware could yield different precisions
+        # On AMD Radeon Pro 5500M, 1e-6 works fine...
+        # https://github.com/taichi-dev/taichi/pull/1779
+        return 1e-4
+    return 1e-6
+
+
 def approx(expected, **kwargs):
     '''Tweaked pytest.approx for OpenGL low percisions'''
     import pytest
@@ -19,11 +31,7 @@ def __ne__(self, other):
     if isinstance(expected, bool):
         return boolean_integer(expected)
 
-    if ti.cfg.arch == ti.opengl:
-        kwargs['rel'] = max(kwargs.get('rel', 1e-6), 1e-3)
-
-    if ti.cfg.arch == ti.metal:
-        kwargs['rel'] = max(kwargs.get('rel', 1e-6), 1e-4)
+    kwargs['rel'] = max(kwargs.get('rel', 1e-6), get_rel_eps())
 
     return pytest.approx(expected, **kwargs)
 
@@ -109,6 +117,7 @@ def wrapped(*args, **kwargs):
 
 
 __all__ = [
+    'get_rel_eps',
     'approx',
     'allclose',
     'make_temp_file',

tests/python/test_test.py

@@ -75,7 +75,7 @@ def test_require_extensions_2():
 @pytest.mark.parametrize('allclose',
                          [ti.allclose, lambda x, y: x == ti.approx(y)])
 def test_allclose_rel(x, allclose):
-    rel = 1e-3 if ti.cfg.arch == ti.opengl else 1e-6
+    rel = ti.get_rel_eps()
     assert not allclose(x + x * rel * 3.0, x)
     assert not allclose(x + x * rel * 1.2, x)
     assert allclose(x + x * rel * 0.9, x)
@@ -92,7 +92,7 @@ def test_allclose_rel(x, allclose):
 @pytest.mark.parametrize('allclose',
                          [ti.allclose, lambda x, y: x == ti.approx(y)])
 def test_allclose_rel_reordered1(x, allclose):
-    rel = 1e-3 if ti.cfg.arch == ti.opengl else 1e-6
+    rel = ti.get_rel_eps()
     assert not allclose(x + x * rel * 3.0, x)
     assert not allclose(x + x * rel * 1.2, x)
     assert allclose(x + x * rel * 0.9, x)
@@ -109,7 +109,7 @@ def test_allclose_rel_reordered1(x, allclose):
                          [ti.allclose, lambda x, y: x == ti.approx(y)])
 @ti.test()
 def test_allclose_rel_reordered2(x, allclose):
-    rel = 1e-3 if ti.cfg.arch == ti.opengl else 1e-6
+    rel = ti.get_rel_eps()
     assert not allclose(x + x * rel * 3.0, x)
     assert not allclose(x + x * rel * 1.2, x)
     assert allclose(x + x * rel * 0.9, x)