[Test] Add missing test for fast erf (apache#6058)

* add missing test for fast erf

* trigger ci

tests/python/relay/test_pass_fast_math.py

@@ -47,6 +47,21 @@ def test_tanh():
         fast_mod = relay.optimize(mod, target='llvm', params=None)
     assert "fast_tanh" in fast_mod[0].astext()
 
+def test_erf():
+    x = relay.var("x", shape=(1, 16, 16, 16), dtype="float32")
+    y = relay.erf(x)
+    func = relay.Function([x], y)
+    mod = tvm.IRModule.from_expr(func)
+
+    fast_mod = FastMath()(mod)
+    assert "fast_erf" in fast_mod.astext()
+
+    # Check that FastMath option works for relay.build.
+    with tvm.transform.PassContext(opt_level=3, required_pass=['FastMath']):
+        fast_mod = relay.optimize(mod, target='llvm', params=None)
+    assert "fast_erf" in fast_mod[0].astext()
+
 if __name__ == "__main__":
     test_exp()
     test_tanh()
+    test_erf()