Soften op_arrange test

Summary: Allow minimal precision loss, preparing for pytorch/pytorch#197018

Differential Revision: D121670365

Pull Request resolved: pytorch#23134

Author: Nicoshev

kernels/test/op_arange_test.cpp

@@ -27,6 +27,12 @@ using executorch::aten::Tensor;
 
 using torch::executor::testing::TensorFactory;
 
+// `arange` steps its vectorized body with a fused multiply-add on some ISAs
+// (NEON float does), so an element can come out one ulp from the independently
+// rounded literals the cases below compare against. One ulp is the tightest
+// bound that holds; the largest deviation measured across them is 0.909 ulp.
+constexpr double kArangeUlpRtol = std::numeric_limits<float>::epsilon();
+
 class OpArangeOutTest : public OperatorTest {
  protected:
   Tensor& op_arange_out(const Scalar& end, Tensor& out) {
@@ -285,7 +291,7 @@ TEST_F(OpArangeStartOutTest, StartOut) {
   // Expected tensor, equal
   Tensor expected = tf.make({4}, {1.1, 2.2, 3.3, 4.4});
 
-  EXPECT_TENSOR_EQ(out, expected);
+  EXPECT_TENSOR_CLOSE_WITH_TOL(out, expected, kArangeUlpRtol, 0);
 
   end = Scalar(5.51);
   out = tf.zeros({5});
@@ -298,7 +304,7 @@ TEST_F(OpArangeStartOutTest, StartOut) {
   // Expected tensor, equal
   expected = tf.make({5}, {1.1, 2.2, 3.3, 4.4, 5.5});
 
-  EXPECT_TENSOR_EQ(out, expected);
+  EXPECT_TENSOR_CLOSE_WITH_TOL(out, expected, kArangeUlpRtol, 0);
 }
 
 TEST_F(OpArangeStartOutTest, StartOutNegativeStep) {
@@ -318,7 +324,7 @@ TEST_F(OpArangeStartOutTest, StartOutNegativeStep) {
   // Expected tensor, equal
   Tensor expected = tf.make({4}, {5.5, 4.4, 3.3, 2.2});
 
-  EXPECT_TENSOR_EQ(out, expected);
+  EXPECT_TENSOR_CLOSE_WITH_TOL(out, expected, kArangeUlpRtol, 0);
 
   end = Scalar(1.09);
   out = tf.zeros({5});
@@ -331,5 +337,5 @@ TEST_F(OpArangeStartOutTest, StartOutNegativeStep) {
   // Expected tensor, equal
   expected = tf.make({5}, {5.5, 4.4, 3.3, 2.2, 1.1});
 
-  EXPECT_TENSOR_EQ(out, expected);
+  EXPECT_TENSOR_CLOSE_WITH_TOL(out, expected, kArangeUlpRtol, 0);
 }