sage.rings.valuation.mapped_valuation_test: add pytests

Copy two TestSuite() runs from a TESTS:: block to pytest. These are on
the verge of hitting the "slow doctest" limit for long tests, and
sometimes cause warnings in the CI. But more importantly, they are
simply better suited to pytest: the user would never want to run them,
and the output is not meaningful as documentation.

Author: orlitzky

src/sage/rings/valuation/mapped_valuation_test.py

@@ -0,0 +1,27 @@
+import pytest
+
+
+def test_finite_extension_from_limit_valuation():
+    r"""
+    Run the ``TestSuite()`` for two examples given in the
+    ``FiniteExtensionFromLimitValuation`` documentation.
+    """
+    from sage.misc.sage_unittest import TestSuite
+    from sage.rings.function_field.constructor import FunctionField
+    from sage.rings.polynomial.polynomial_ring_constructor import PolynomialRing
+    from sage.rings.integer import Integer
+    from sage.rings.rational_field import QQ
+
+    K = FunctionField(QQ, 'x')
+    x = K.gen()
+    R = PolynomialRing(K, 'y')
+    y = R.gen()
+    L = K.extension(y**2 - x)
+    v = K.valuation(Integer(1))
+    w = v.extensions(L)
+
+    for ext in w:
+        # fewer max_runs, these are kind of slow
+        TestSuite(ext).run(verbose=True,
+                           raise_on_failure=True,
+                           max_runs=512)