TST: special: small improvements to Wright Omega tests

- Use a smaller range for the systematic tests since the asymptotic
  regimes are simpler
- Use `assert_func_equal` for the real vs. complex implementation
  tests to get better error reporting

scipy/special/tests/test_mpmath.py

@@ -1856,11 +1856,14 @@ def test_wrightomega_real(self):
         def mpmath_wrightomega_real(x):
             return mpmath.lambertw(mpmath.exp(x), mpmath.mpf('-0.5'))
 
+        # For x < -1000 the Wright Omega function is just 0 to double
+        # precision, and for x > 1e21 it is just x to double
+        # precision.
         assert_mpmath_equal(
             sc.wrightomega,
             mpmath_wrightomega_real,
-            [Arg()],
-            rtol=1e-15,
+            [Arg(-1000, 1e21)],
+            rtol=5e-15,
             atol=0,
             nan_ok=False,
         )

scipy/special/tests/test_wrightomega.py

@@ -5,6 +5,7 @@
 from numpy.testing import assert_, assert_equal, assert_allclose
 
 import scipy.special as sc
+from scipy.special._testutils import assert_func_equal
 
 
 def test_wrightomega_nan():
@@ -114,9 +115,5 @@ def test_wrightomega_exp_approximation_crossover():
 
 def test_wrightomega_real_versus_complex():
     x = np.linspace(-500, 500, 1001)
-    assert_allclose(
-        sc.wrightomega(x),
-        sc.wrightomega(x + 0j).real,
-        atol=0,
-        rtol=1e-14,
-    )
+    results = sc.wrightomega(x + 0j).real
+    assert_func_equal(sc.wrightomega, results, x, atol=0, rtol=1e-15)