Port tests to pytest

Use simple asserts and pytest's powerful introspection to make testing
simpler. This merges the old .py/.ref file pairs into simple .py files
where the expected values are right next to the code being tested.

This commit does not touch the C++ part of the code and replicates the
Python tests exactly like the old .ref-file-based approach.

tests/test_methods_and_attributes.cpp

@@ -0,0 +1,84 @@
+/*
+    tests/test_methods_and_attributes.cpp -- constructors, deconstructors, attribute access,
+    __str__, argument and return value conventions
+
+    Copyright (c) 2016 Wenzel Jakob <wenzel.jakob@epfl.ch>
+
+    All rights reserved. Use of this source code is governed by a
+    BSD-style license that can be found in the LICENSE file.
+*/
+
+#include "pybind11_tests.h"
+#include "constructor_stats.h"
+
+class ExampleMandA {
+public:
+    ExampleMandA() { print_default_created(this); }
+    ExampleMandA(int value) : value(value) { print_created(this, value); }
+    ExampleMandA(const ExampleMandA &e) : value(e.value) { print_copy_created(this); }
+    ExampleMandA(ExampleMandA &&e) : value(e.value) { print_move_created(this); }
+    ~ExampleMandA() { print_destroyed(this); }
+
+    std::string toString() {
+        return "ExampleMandA[value=" + std::to_string(value) + "]";
+    }
+
+    void operator=(const ExampleMandA &e) { print_copy_assigned(this); value = e.value; }
+    void operator=(ExampleMandA &&e) { print_move_assigned(this); value = e.value; }
+
+    void add1(ExampleMandA other) { value += other.value; }           // passing by value
+    void add2(ExampleMandA &other) { value += other.value; }          // passing by reference
+    void add3(const ExampleMandA &other) { value += other.value; }    // passing by const reference
+    void add4(ExampleMandA *other) { value += other->value; }         // passing by pointer
+    void add5(const ExampleMandA *other) { value += other->value; }   // passing by const pointer
+
+    void add6(int other) { value += other; }                      // passing by value
+    void add7(int &other) { value += other; }                     // passing by reference
+    void add8(const int &other) { value += other; }               // passing by const reference
+    void add9(int *other) { value += *other; }                    // passing by pointer
+    void add10(const int *other) { value += *other; }             // passing by const pointer
+
+    ExampleMandA self1() { return *this; }                            // return by value
+    ExampleMandA &self2() { return *this; }                           // return by reference
+    const ExampleMandA &self3() { return *this; }                     // return by const reference
+    ExampleMandA *self4() { return this; }                            // return by pointer
+    const ExampleMandA *self5() { return this; }                      // return by const pointer
+
+    int internal1() { return value; }                             // return by value
+    int &internal2() { return value; }                            // return by reference
+    const int &internal3() { return value; }                      // return by const reference
+    int *internal4() { return &value; }                           // return by pointer
+    const int *internal5() { return &value; }                     // return by const pointer
+
+    int value = 0;
+};
+
+void init_ex_methods_and_attributes(py::module &m) {
+    py::class_<ExampleMandA>(m, "ExampleMandA")
+        .def(py::init<>())
+        .def(py::init<int>())
+        .def(py::init<const ExampleMandA&>())
+        .def("add1", &ExampleMandA::add1)
+        .def("add2", &ExampleMandA::add2)
+        .def("add3", &ExampleMandA::add3)
+        .def("add4", &ExampleMandA::add4)
+        .def("add5", &ExampleMandA::add5)
+        .def("add6", &ExampleMandA::add6)
+        .def("add7", &ExampleMandA::add7)
+        .def("add8", &ExampleMandA::add8)
+        .def("add9", &ExampleMandA::add9)
+        .def("add10", &ExampleMandA::add10)
+        .def("self1", &ExampleMandA::self1)
+        .def("self2", &ExampleMandA::self2)
+        .def("self3", &ExampleMandA::self3)
+        .def("self4", &ExampleMandA::self4)
+        .def("self5", &ExampleMandA::self5)
+        .def("internal1", &ExampleMandA::internal1)
+        .def("internal2", &ExampleMandA::internal2)
+        .def("internal3", &ExampleMandA::internal3)
+        .def("internal4", &ExampleMandA::internal4)
+        .def("internal5", &ExampleMandA::internal5)
+        .def("__str__", &ExampleMandA::toString)
+        .def_readwrite("value", &ExampleMandA::value)
+        ;
+}