Move enum tests into a new file

There are more enum tests than 'constants and functions'.

tests/test_enum.py

@@ -0,0 +1,63 @@
+import pytest
+
+
+def test_unscoped_enum():
+    from pybind11_tests import UnscopedEnum, EOne
+
+    assert str(UnscopedEnum.EOne) == "UnscopedEnum.EOne"
+    assert str(UnscopedEnum.ETwo) == "UnscopedEnum.ETwo"
+    assert str(EOne) == "UnscopedEnum.EOne"
+
+    # no TypeError exception for unscoped enum ==/!= int comparisons
+    y = UnscopedEnum.ETwo
+    assert y == 2
+    assert y != 3
+
+    assert int(UnscopedEnum.ETwo) == 2
+    assert str(UnscopedEnum(2)) == "UnscopedEnum.ETwo"
+
+
+def test_scoped_enum():
+    from pybind11_tests import ScopedEnum, test_scoped_enum
+
+    assert test_scoped_enum(ScopedEnum.Three) == "ScopedEnum::Three"
+    z = ScopedEnum.Two
+    assert test_scoped_enum(z) == "ScopedEnum::Two"
+
+    # expected TypeError exceptions for scoped enum ==/!= int comparisons
+    with pytest.raises(TypeError):
+        assert z == 2
+    with pytest.raises(TypeError):
+        assert z != 3
+
+
+def test_implicit_conversion():
+    from pybind11_tests import ClassWithUnscopedEnum
+
+    assert str(ClassWithUnscopedEnum.EMode.EFirstMode) == "EMode.EFirstMode"
+    assert str(ClassWithUnscopedEnum.EFirstMode) == "EMode.EFirstMode"
+
+    f = ClassWithUnscopedEnum.test_function
+    first = ClassWithUnscopedEnum.EFirstMode
+    second = ClassWithUnscopedEnum.ESecondMode
+
+    assert f(first) == 1
+
+    assert f(first) == f(first)
+    assert not f(first) != f(first)
+
+    assert f(first) != f(second)
+    assert not f(first) == f(second)
+
+    assert f(first) == int(f(first))
+    assert not f(first) != int(f(first))
+
+    assert f(first) != int(f(second))
+    assert not f(first) == int(f(second))
+
+    # noinspection PyDictCreation
+    x = {f(first): 1, f(second): 2}
+    x[f(first)] = 3
+    x[f(second)] = 4
+    # Hashing test
+    assert str(x) == "{EMode.EFirstMode: 3, EMode.ESecondMode: 4}"