Serialize/deserialize chained exceptions (#5787)

Serialize/deserialize chained exceptions

changelog/5786.bugfix.rst

@@ -0,0 +1,2 @@
+Chained exceptions in test and collection reports are now correctly serialized, allowing plugins like
+``pytest-xdist`` to display them properly.

src/_pytest/reports.py

@@ -3,6 +3,7 @@ from typing import Optional
 
 import py
 
+from _pytest._code.code import ExceptionChainRepr
 from _pytest._code.code import ExceptionInfo
 from _pytest._code.code import ReprEntry
 from _pytest._code.code import ReprEntryNative
@@ -160,46 +161,7 @@ class BaseReport:
 
         Experimental method.
         """
-
+        return _report_to_json(self)
-        def disassembled_report(rep):
-            reprtraceback = rep.longrepr.reprtraceback.__dict__.copy()
-            reprcrash = rep.longrepr.reprcrash.__dict__.copy()
-
-            new_entries = []
-            for entry in reprtraceback["reprentries"]:
-                entry_data = {
-                    "type": type(entry).__name__,
-                    "data": entry.__dict__.copy(),
-                }
-                for key, value in entry_data["data"].items():
-                    if hasattr(value, "__dict__"):
-                        entry_data["data"][key] = value.__dict__.copy()
-                new_entries.append(entry_data)
-
-            reprtraceback["reprentries"] = new_entries
-
-            return {
-                "reprcrash": reprcrash,
-                "reprtraceback": reprtraceback,
-                "sections": rep.longrepr.sections,
-            }
-
-        d = self.__dict__.copy()
-        if hasattr(self.longrepr, "toterminal"):
-            if hasattr(self.longrepr, "reprtraceback") and hasattr(
-                self.longrepr, "reprcrash"
-            ):
-                d["longrepr"] = disassembled_report(self)
-            else:
-                d["longrepr"] = str(self.longrepr)
-        else:
-            d["longrepr"] = self.longrepr
-        for name in d:
-            if isinstance(d[name], (py.path.local, Path)):
-                d[name] = str(d[name])
-            elif name == "result":
-                d[name] = None  # for now
-        return d
 
     @classmethod
     def _from_json(cls, reportdict):
@@ -211,55 +173,8 @@ class BaseReport:
 
         Experimental method.
         """
-        if reportdict["longrepr"]:
+        kwargs = _report_kwargs_from_json(reportdict)
-            if (
+        return cls(**kwargs)
-                "reprcrash" in reportdict["longrepr"]
-                and "reprtraceback" in reportdict["longrepr"]
-            ):
-
-                reprtraceback = reportdict["longrepr"]["reprtraceback"]
-                reprcrash = reportdict["longrepr"]["reprcrash"]
-
-                unserialized_entries = []
-                reprentry = None
-                for entry_data in reprtraceback["reprentries"]:
-                    data = entry_data["data"]
-                    entry_type = entry_data["type"]
-                    if entry_type == "ReprEntry":
-                        reprfuncargs = None
-                        reprfileloc = None
-                        reprlocals = None
-                        if data["reprfuncargs"]:
-                            reprfuncargs = ReprFuncArgs(**data["reprfuncargs"])
-                        if data["reprfileloc"]:
-                            reprfileloc = ReprFileLocation(**data["reprfileloc"])
-                        if data["reprlocals"]:
-                            reprlocals = ReprLocals(data["reprlocals"]["lines"])
-
-                        reprentry = ReprEntry(
-                            lines=data["lines"],
-                            reprfuncargs=reprfuncargs,
-                            reprlocals=reprlocals,
-                            filelocrepr=reprfileloc,
-                            style=data["style"],
-                        )
-                    elif entry_type == "ReprEntryNative":
-                        reprentry = ReprEntryNative(data["lines"])
-                    else:
-                        _report_unserialization_failure(entry_type, cls, reportdict)
-                    unserialized_entries.append(reprentry)
-                reprtraceback["reprentries"] = unserialized_entries
-
-                exception_info = ReprExceptionInfo(
-                    reprtraceback=ReprTraceback(**reprtraceback),
-                    reprcrash=ReprFileLocation(**reprcrash),
-                )
-
-                for section in reportdict["longrepr"]["sections"]:
-                    exception_info.addsection(*section)
-                reportdict["longrepr"] = exception_info
-
-        return cls(**reportdict)
 
 
 def _report_unserialization_failure(type_name, report_class, reportdict):
@@ -424,3 +339,142 @@ def pytest_report_from_serializable(data):
         assert False, "Unknown report_type unserialize data: {}".format(
             data["_report_type"]
         )
+
+
+def _report_to_json(report):
+    """
+    This was originally the serialize_report() function from xdist (ca03269).
+
+    Returns the contents of this report as a dict of builtin entries, suitable for
+    serialization.
+    """
+
+    def serialize_repr_entry(entry):
+        entry_data = {"type": type(entry).__name__, "data": entry.__dict__.copy()}
+        for key, value in entry_data["data"].items():
+            if hasattr(value, "__dict__"):
+                entry_data["data"][key] = value.__dict__.copy()
+        return entry_data
+
+    def serialize_repr_traceback(reprtraceback):
+        result = reprtraceback.__dict__.copy()
+        result["reprentries"] = [
+            serialize_repr_entry(x) for x in reprtraceback.reprentries
+        ]
+        return result
+
+    def serialize_repr_crash(reprcrash):
+        return reprcrash.__dict__.copy()
+
+    def serialize_longrepr(rep):
+        result = {
+            "reprcrash": serialize_repr_crash(rep.longrepr.reprcrash),
+            "reprtraceback": serialize_repr_traceback(rep.longrepr.reprtraceback),
+            "sections": rep.longrepr.sections,
+        }
+        if isinstance(rep.longrepr, ExceptionChainRepr):
+            result["chain"] = []
+            for repr_traceback, repr_crash, description in rep.longrepr.chain:
+                result["chain"].append(
+                    (
+                        serialize_repr_traceback(repr_traceback),
+                        serialize_repr_crash(repr_crash),
+                        description,
+                    )
+                )
+        else:
+            result["chain"] = None
+        return result
+
+    d = report.__dict__.copy()
+    if hasattr(report.longrepr, "toterminal"):
+        if hasattr(report.longrepr, "reprtraceback") and hasattr(
+            report.longrepr, "reprcrash"
+        ):
+            d["longrepr"] = serialize_longrepr(report)
+        else:
+            d["longrepr"] = str(report.longrepr)
+    else:
+        d["longrepr"] = report.longrepr
+    for name in d:
+        if isinstance(d[name], (py.path.local, Path)):
+            d[name] = str(d[name])
+        elif name == "result":
+            d[name] = None  # for now
+    return d
+
+
+def _report_kwargs_from_json(reportdict):
+    """
+    This was originally the serialize_report() function from xdist (ca03269).
+
+    Returns **kwargs that can be used to construct a TestReport or CollectReport instance.
+    """
+
+    def deserialize_repr_entry(entry_data):
+        data = entry_data["data"]
+        entry_type = entry_data["type"]
+        if entry_type == "ReprEntry":
+            reprfuncargs = None
+            reprfileloc = None
+            reprlocals = None
+            if data["reprfuncargs"]:
+                reprfuncargs = ReprFuncArgs(**data["reprfuncargs"])
+            if data["reprfileloc"]:
+                reprfileloc = ReprFileLocation(**data["reprfileloc"])
+            if data["reprlocals"]:
+                reprlocals = ReprLocals(data["reprlocals"]["lines"])
+
+            reprentry = ReprEntry(
+                lines=data["lines"],
+                reprfuncargs=reprfuncargs,
+                reprlocals=reprlocals,
+                filelocrepr=reprfileloc,
+                style=data["style"],
+            )
+        elif entry_type == "ReprEntryNative":
+            reprentry = ReprEntryNative(data["lines"])
+        else:
+            _report_unserialization_failure(entry_type, TestReport, reportdict)
+        return reprentry
+
+    def deserialize_repr_traceback(repr_traceback_dict):
+        repr_traceback_dict["reprentries"] = [
+            deserialize_repr_entry(x) for x in repr_traceback_dict["reprentries"]
+        ]
+        return ReprTraceback(**repr_traceback_dict)
+
+    def deserialize_repr_crash(repr_crash_dict):
+        return ReprFileLocation(**repr_crash_dict)
+
+    if (
+        reportdict["longrepr"]
+        and "reprcrash" in reportdict["longrepr"]
+        and "reprtraceback" in reportdict["longrepr"]
+    ):
+
+        reprtraceback = deserialize_repr_traceback(
+            reportdict["longrepr"]["reprtraceback"]
+        )
+        reprcrash = deserialize_repr_crash(reportdict["longrepr"]["reprcrash"])
+        if reportdict["longrepr"]["chain"]:
+            chain = []
+            for repr_traceback_data, repr_crash_data, description in reportdict[
+                "longrepr"
+            ]["chain"]:
+                chain.append(
+                    (
+                        deserialize_repr_traceback(repr_traceback_data),
+                        deserialize_repr_crash(repr_crash_data),
+                        description,
+                    )
+                )
+            exception_info = ExceptionChainRepr(chain)
+        else:
+            exception_info = ReprExceptionInfo(reprtraceback, reprcrash)
+
+        for section in reportdict["longrepr"]["sections"]:
+            exception_info.addsection(*section)
+        reportdict["longrepr"] = exception_info
+
+    return reportdict

testing/code/test_code.py

@@ -1,8 +1,6 @@
 import sys
 from unittest import mock
 
-from test_excinfo import TWMock
-
 import _pytest._code
 import pytest
 
@@ -168,17 +166,15 @@ class TestTracebackEntry:
 
 
 class TestReprFuncArgs:
-    def test_not_raise_exception_with_mixed_encoding(self):
+    def test_not_raise_exception_with_mixed_encoding(self, tw_mock):
         from _pytest._code.code import ReprFuncArgs
 
-        tw = TWMock()
-
         args = [("unicode_string", "São Paulo"), ("utf8_string", b"S\xc3\xa3o Paulo")]
 
         r = ReprFuncArgs(args)
-        r.toterminal(tw)
+        r.toterminal(tw_mock)
 
         assert (
-            tw.lines[0]
+            tw_mock.lines[0]
             == r"unicode_string = São Paulo, utf8_string = b'S\xc3\xa3o Paulo'"
         )

testing/code/test_excinfo.py

@@ -31,33 +31,6 @@ def limited_recursion_depth():
     sys.setrecursionlimit(before)
 
 
-class TWMock:
-    WRITE = object()
-
-    def __init__(self):
-        self.lines = []
-        self.is_writing = False
-
-    def sep(self, sep, line=None):
-        self.lines.append((sep, line))
-
-    def write(self, msg, **kw):
-        self.lines.append((TWMock.WRITE, msg))
-
-    def line(self, line, **kw):
-        self.lines.append(line)
-
-    def markup(self, text, **kw):
-        return text
-
-    def get_write_msg(self, idx):
-        flag, msg = self.lines[idx]
-        assert flag == TWMock.WRITE
-        return msg
-
-    fullwidth = 80
-
-
 def test_excinfo_simple() -> None:
     try:
         raise ValueError
@@ -658,7 +631,7 @@ raise ValueError()
         assert loc.lineno == 3
         # assert loc.message == "ValueError: hello"
 
-    def test_repr_tracebackentry_lines2(self, importasmod):
+    def test_repr_tracebackentry_lines2(self, importasmod, tw_mock):
         mod = importasmod(
             """
             def func1(m, x, y, z):
@@ -678,13 +651,12 @@ raise ValueError()
         p = FormattedExcinfo(funcargs=True)
         repr_entry = p.repr_traceback_entry(entry)
         assert repr_entry.reprfuncargs.args == reprfuncargs.args
-        tw = TWMock()
+        repr_entry.toterminal(tw_mock)
-        repr_entry.toterminal(tw)
+        assert tw_mock.lines[0] == "m = " + repr("m" * 90)
-        assert tw.lines[0] == "m = " + repr("m" * 90)
+        assert tw_mock.lines[1] == "x = 5, y = 13"
-        assert tw.lines[1] == "x = 5, y = 13"
+        assert tw_mock.lines[2] == "z = " + repr("z" * 120)
-        assert tw.lines[2] == "z = " + repr("z" * 120)
 
-    def test_repr_tracebackentry_lines_var_kw_args(self, importasmod):
+    def test_repr_tracebackentry_lines_var_kw_args(self, importasmod, tw_mock):
         mod = importasmod(
             """
             def func1(x, *y, **z):
@@ -703,9 +675,8 @@ raise ValueError()
         p = FormattedExcinfo(funcargs=True)
         repr_entry = p.repr_traceback_entry(entry)
         assert repr_entry.reprfuncargs.args == reprfuncargs.args
-        tw = TWMock()
+        repr_entry.toterminal(tw_mock)
-        repr_entry.toterminal(tw)
+        assert tw_mock.lines[0] == "x = 'a', y = ('b',), z = {'c': 'd'}"
-        assert tw.lines[0] == "x = 'a', y = ('b',), z = {'c': 'd'}"
 
     def test_repr_tracebackentry_short(self, importasmod):
         mod = importasmod(
@@ -842,7 +813,7 @@ raise ValueError()
         assert p._makepath(__file__) == __file__
         p.repr_traceback(excinfo)
 
-    def test_repr_excinfo_addouterr(self, importasmod):
+    def test_repr_excinfo_addouterr(self, importasmod, tw_mock):
         mod = importasmod(
             """
             def entry():
@@ -852,10 +823,9 @@ raise ValueError()
         excinfo = pytest.raises(ValueError, mod.entry)
         repr = excinfo.getrepr()
         repr.addsection("title", "content")
-        twmock = TWMock()
+        repr.toterminal(tw_mock)
-        repr.toterminal(twmock)
+        assert tw_mock.lines[-1] == "content"
-        assert twmock.lines[-1] == "content"
+        assert tw_mock.lines[-2] == ("-", "title")
-        assert twmock.lines[-2] == ("-", "title")
 
     def test_repr_excinfo_reprcrash(self, importasmod):
         mod = importasmod(
@@ -920,7 +890,7 @@ raise ValueError()
         x = str(MyRepr())
         assert x == "я"
 
-    def test_toterminal_long(self, importasmod):
+    def test_toterminal_long(self, importasmod, tw_mock):
         mod = importasmod(
             """
             def g(x):
@@ -932,27 +902,26 @@ raise ValueError()
         excinfo = pytest.raises(ValueError, mod.f)
         excinfo.traceback = excinfo.traceback.filter()
         repr = excinfo.getrepr()
-        tw = TWMock()
+        repr.toterminal(tw_mock)
-        repr.toterminal(tw)
+        assert tw_mock.lines[0] == ""
-        assert tw.lines[0] == ""
+        tw_mock.lines.pop(0)
-        tw.lines.pop(0)
+        assert tw_mock.lines[0] == "    def f():"
-        assert tw.lines[0] == "    def f():"
+        assert tw_mock.lines[1] == ">       g(3)"
-        assert tw.lines[1] == ">       g(3)"
+        assert tw_mock.lines[2] == ""
-        assert tw.lines[2] == ""
+        line = tw_mock.get_write_msg(3)
-        line = tw.get_write_msg(3)
         assert line.endswith("mod.py")
-        assert tw.lines[4] == (":5: ")
+        assert tw_mock.lines[4] == (":5: ")
-        assert tw.lines[5] == ("_ ", None)
+        assert tw_mock.lines[5] == ("_ ", None)
-        assert tw.lines[6] == ""
+        assert tw_mock.lines[6] == ""
-        assert tw.lines[7] == "    def g(x):"
+        assert tw_mock.lines[7] == "    def g(x):"
-        assert tw.lines[8] == ">       raise ValueError(x)"
+        assert tw_mock.lines[8] == ">       raise ValueError(x)"
-        assert tw.lines[9] == "E       ValueError: 3"
+        assert tw_mock.lines[9] == "E       ValueError: 3"
-        assert tw.lines[10] == ""
+        assert tw_mock.lines[10] == ""
-        line = tw.get_write_msg(11)
+        line = tw_mock.get_write_msg(11)
         assert line.endswith("mod.py")
-        assert tw.lines[12] == ":3: ValueError"
+        assert tw_mock.lines[12] == ":3: ValueError"
 
-    def test_toterminal_long_missing_source(self, importasmod, tmpdir):
+    def test_toterminal_long_missing_source(self, importasmod, tmpdir, tw_mock):
         mod = importasmod(
             """
             def g(x):
@@ -965,25 +934,24 @@ raise ValueError()
         tmpdir.join("mod.py").remove()
         excinfo.traceback = excinfo.traceback.filter()
         repr = excinfo.getrepr()
-        tw = TWMock()
+        repr.toterminal(tw_mock)
-        repr.toterminal(tw)
+        assert tw_mock.lines[0] == ""
-        assert tw.lines[0] == ""
+        tw_mock.lines.pop(0)
-        tw.lines.pop(0)
+        assert tw_mock.lines[0] == ">   ???"
-        assert tw.lines[0] == ">   ???"
+        assert tw_mock.lines[1] == ""
-        assert tw.lines[1] == ""
+        line = tw_mock.get_write_msg(2)
-        line = tw.get_write_msg(2)
         assert line.endswith("mod.py")
-        assert tw.lines[3] == ":5: "
+        assert tw_mock.lines[3] == ":5: "
-        assert tw.lines[4] == ("_ ", None)
+        assert tw_mock.lines[4] == ("_ ", None)
-        assert tw.lines[5] == ""
+        assert tw_mock.lines[5] == ""
-        assert tw.lines[6] == ">   ???"
+        assert tw_mock.lines[6] == ">   ???"
-        assert tw.lines[7] == "E   ValueError: 3"
+        assert tw_mock.lines[7] == "E   ValueError: 3"
-        assert tw.lines[8] == ""
+        assert tw_mock.lines[8] == ""
-        line = tw.get_write_msg(9)
+        line = tw_mock.get_write_msg(9)
         assert line.endswith("mod.py")
-        assert tw.lines[10] == ":3: ValueError"
+        assert tw_mock.lines[10] == ":3: ValueError"
 
-    def test_toterminal_long_incomplete_source(self, importasmod, tmpdir):
+    def test_toterminal_long_incomplete_source(self, importasmod, tmpdir, tw_mock):
         mod = importasmod(
             """
             def g(x):
@@ -996,25 +964,24 @@ raise ValueError()
         tmpdir.join("mod.py").write("asdf")
         excinfo.traceback = excinfo.traceback.filter()
         repr = excinfo.getrepr()
-        tw = TWMock()
+        repr.toterminal(tw_mock)
-        repr.toterminal(tw)
+        assert tw_mock.lines[0] == ""
-        assert tw.lines[0] == ""
+        tw_mock.lines.pop(0)
-        tw.lines.pop(0)
+        assert tw_mock.lines[0] == ">   ???"
-        assert tw.lines[0] == ">   ???"
+        assert tw_mock.lines[1] == ""
-        assert tw.lines[1] == ""
+        line = tw_mock.get_write_msg(2)
-        line = tw.get_write_msg(2)
         assert line.endswith("mod.py")
-        assert tw.lines[3] == ":5: "
+        assert tw_mock.lines[3] == ":5: "
-        assert tw.lines[4] == ("_ ", None)
+        assert tw_mock.lines[4] == ("_ ", None)
-        assert tw.lines[5] == ""
+        assert tw_mock.lines[5] == ""
-        assert tw.lines[6] == ">   ???"
+        assert tw_mock.lines[6] == ">   ???"
-        assert tw.lines[7] == "E   ValueError: 3"
+        assert tw_mock.lines[7] == "E   ValueError: 3"
-        assert tw.lines[8] == ""
+        assert tw_mock.lines[8] == ""
-        line = tw.get_write_msg(9)
+        line = tw_mock.get_write_msg(9)
         assert line.endswith("mod.py")
-        assert tw.lines[10] == ":3: ValueError"
+        assert tw_mock.lines[10] == ":3: ValueError"
 
-    def test_toterminal_long_filenames(self, importasmod):
+    def test_toterminal_long_filenames(self, importasmod, tw_mock):
         mod = importasmod(
             """
             def f():
@@ -1022,23 +989,22 @@ raise ValueError()
         """
         )
         excinfo = pytest.raises(ValueError, mod.f)
-        tw = TWMock()
         path = py.path.local(mod.__file__)
         old = path.dirpath().chdir()
         try:
             repr = excinfo.getrepr(abspath=False)
-            repr.toterminal(tw)
+            repr.toterminal(tw_mock)
             x = py.path.local().bestrelpath(path)
             if len(x) < len(str(path)):
-                msg = tw.get_write_msg(-2)
+                msg = tw_mock.get_write_msg(-2)
                 assert msg == "mod.py"
-                assert tw.lines[-1] == ":3: ValueError"
+                assert tw_mock.lines[-1] == ":3: ValueError"
 
             repr = excinfo.getrepr(abspath=True)
-            repr.toterminal(tw)
+            repr.toterminal(tw_mock)
-            msg = tw.get_write_msg(-2)
+            msg = tw_mock.get_write_msg(-2)
             assert msg == path
-            line = tw.lines[-1]
+            line = tw_mock.lines[-1]
             assert line == ":3: ValueError"
         finally:
             old.chdir()
@@ -1073,7 +1039,7 @@ raise ValueError()
         repr.toterminal(tw)
         assert tw.stringio.getvalue()
 
-    def test_traceback_repr_style(self, importasmod):
+    def test_traceback_repr_style(self, importasmod, tw_mock):
         mod = importasmod(
             """
             def f():
@@ -1091,35 +1057,34 @@ raise ValueError()
         excinfo.traceback[1].set_repr_style("short")
         excinfo.traceback[2].set_repr_style("short")
         r = excinfo.getrepr(style="long")
-        tw = TWMock()
+        r.toterminal(tw_mock)
-        r.toterminal(tw)
+        for line in tw_mock.lines:
-        for line in tw.lines:
             print(line)
-        assert tw.lines[0] == ""
+        assert tw_mock.lines[0] == ""
-        assert tw.lines[1] == "    def f():"
+        assert tw_mock.lines[1] == "    def f():"
-        assert tw.lines[2] == ">       g()"
+        assert tw_mock.lines[2] == ">       g()"
-        assert tw.lines[3] == ""
+        assert tw_mock.lines[3] == ""
-        msg = tw.get_write_msg(4)
+        msg = tw_mock.get_write_msg(4)
         assert msg.endswith("mod.py")
-        assert tw.lines[5] == ":3: "
+        assert tw_mock.lines[5] == ":3: "
-        assert tw.lines[6] == ("_ ", None)
+        assert tw_mock.lines[6] == ("_ ", None)
-        tw.get_write_msg(7)
+        tw_mock.get_write_msg(7)
-        assert tw.lines[8].endswith("in g")
+        assert tw_mock.lines[8].endswith("in g")
-        assert tw.lines[9] == "    h()"
+        assert tw_mock.lines[9] == "    h()"
-        tw.get_write_msg(10)
+        tw_mock.get_write_msg(10)
-        assert tw.lines[11].endswith("in h")
+        assert tw_mock.lines[11].endswith("in h")
-        assert tw.lines[12] == "    i()"
+        assert tw_mock.lines[12] == "    i()"
-        assert tw.lines[13] == ("_ ", None)
+        assert tw_mock.lines[13] == ("_ ", None)
-        assert tw.lines[14] == ""
+        assert tw_mock.lines[14] == ""
-        assert tw.lines[15] == "    def i():"
+        assert tw_mock.lines[15] == "    def i():"
-        assert tw.lines[16] == ">       raise ValueError()"
+        assert tw_mock.lines[16] == ">       raise ValueError()"
-        assert tw.lines[17] == "E       ValueError"
+        assert tw_mock.lines[17] == "E       ValueError"
-        assert tw.lines[18] == ""
+        assert tw_mock.lines[18] == ""
-        msg = tw.get_write_msg(19)
+        msg = tw_mock.get_write_msg(19)
         msg.endswith("mod.py")
-        assert tw.lines[20] == ":9: ValueError"
+        assert tw_mock.lines[20] == ":9: ValueError"
 
-    def test_exc_chain_repr(self, importasmod):
+    def test_exc_chain_repr(self, importasmod, tw_mock):
         mod = importasmod(
             """
             class Err(Exception):
@@ -1140,72 +1105,71 @@ raise ValueError()
         )
         excinfo = pytest.raises(AttributeError, mod.f)
         r = excinfo.getrepr(style="long")
-        tw = TWMock()
+        r.toterminal(tw_mock)
-        r.toterminal(tw)
+        for line in tw_mock.lines:
-        for line in tw.lines:
             print(line)
-        assert tw.lines[0] == ""
+        assert tw_mock.lines[0] == ""
-        assert tw.lines[1] == "    def f():"
+        assert tw_mock.lines[1] == "    def f():"
-        assert tw.lines[2] == "        try:"
+        assert tw_mock.lines[2] == "        try:"
-        assert tw.lines[3] == ">           g()"
+        assert tw_mock.lines[3] == ">           g()"
-        assert tw.lines[4] == ""
+        assert tw_mock.lines[4] == ""
-        line = tw.get_write_msg(5)
+        line = tw_mock.get_write_msg(5)
         assert line.endswith("mod.py")
-        assert tw.lines[6] == ":6: "
+        assert tw_mock.lines[6] == ":6: "
-        assert tw.lines[7] == ("_ ", None)
+        assert tw_mock.lines[7] == ("_ ", None)
-        assert tw.lines[8] == ""
+        assert tw_mock.lines[8] == ""
-        assert tw.lines[9] == "    def g():"
+        assert tw_mock.lines[9] == "    def g():"
-        assert tw.lines[10] == ">       raise ValueError()"
+        assert tw_mock.lines[10] == ">       raise ValueError()"
-        assert tw.lines[11] == "E       ValueError"
+        assert tw_mock.lines[11] == "E       ValueError"
-        assert tw.lines[12] == ""
+        assert tw_mock.lines[12] == ""
-        line = tw.get_write_msg(13)
+        line = tw_mock.get_write_msg(13)
         assert line.endswith("mod.py")
-        assert tw.lines[14] == ":12: ValueError"
+        assert tw_mock.lines[14] == ":12: ValueError"
-        assert tw.lines[15] == ""
+        assert tw_mock.lines[15] == ""
         assert (
-            tw.lines[16]
+            tw_mock.lines[16]
             == "The above exception was the direct cause of the following exception:"
         )
-        assert tw.lines[17] == ""
+        assert tw_mock.lines[17] == ""
-        assert tw.lines[18] == "    def f():"
+        assert tw_mock.lines[18] == "    def f():"
-        assert tw.lines[19] == "        try:"
+        assert tw_mock.lines[19] == "        try:"
-        assert tw.lines[20] == "            g()"
+        assert tw_mock.lines[20] == "            g()"
-        assert tw.lines[21] == "        except Exception as e:"
+        assert tw_mock.lines[21] == "        except Exception as e:"
-        assert tw.lines[22] == ">           raise Err() from e"
+        assert tw_mock.lines[22] == ">           raise Err() from e"
-        assert tw.lines[23] == "E           test_exc_chain_repr0.mod.Err"
+        assert tw_mock.lines[23] == "E           test_exc_chain_repr0.mod.Err"
-        assert tw.lines[24] == ""
+        assert tw_mock.lines[24] == ""
-        line = tw.get_write_msg(25)
+        line = tw_mock.get_write_msg(25)
         assert line.endswith("mod.py")
-        assert tw.lines[26] == ":8: Err"
+        assert tw_mock.lines[26] == ":8: Err"
-        assert tw.lines[27] == ""
+        assert tw_mock.lines[27] == ""
         assert (
-            tw.lines[28]
+            tw_mock.lines[28]
             == "During handling of the above exception, another exception occurred:"
         )
-        assert tw.lines[29] == ""
+        assert tw_mock.lines[29] == ""
-        assert tw.lines[30] == "    def f():"
+        assert tw_mock.lines[30] == "    def f():"
-        assert tw.lines[31] == "        try:"
+        assert tw_mock.lines[31] == "        try:"
-        assert tw.lines[32] == "            g()"
+        assert tw_mock.lines[32] == "            g()"
-        assert tw.lines[33] == "        except Exception as e:"
+        assert tw_mock.lines[33] == "        except Exception as e:"
-        assert tw.lines[34] == "            raise Err() from e"
+        assert tw_mock.lines[34] == "            raise Err() from e"
-        assert tw.lines[35] == "        finally:"
+        assert tw_mock.lines[35] == "        finally:"
-        assert tw.lines[36] == ">           h()"
+        assert tw_mock.lines[36] == ">           h()"
-        assert tw.lines[37] == ""
+        assert tw_mock.lines[37] == ""
-        line = tw.get_write_msg(38)
+        line = tw_mock.get_write_msg(38)
         assert line.endswith("mod.py")
-        assert tw.lines[39] == ":10: "
+        assert tw_mock.lines[39] == ":10: "
-        assert tw.lines[40] == ("_ ", None)
+        assert tw_mock.lines[40] == ("_ ", None)
-        assert tw.lines[41] == ""
+        assert tw_mock.lines[41] == ""
-        assert tw.lines[42] == "    def h():"
+        assert tw_mock.lines[42] == "    def h():"
-        assert tw.lines[43] == ">       raise AttributeError()"
+        assert tw_mock.lines[43] == ">       raise AttributeError()"
-        assert tw.lines[44] == "E       AttributeError"
+        assert tw_mock.lines[44] == "E       AttributeError"
-        assert tw.lines[45] == ""
+        assert tw_mock.lines[45] == ""
-        line = tw.get_write_msg(46)
+        line = tw_mock.get_write_msg(46)
         assert line.endswith("mod.py")
-        assert tw.lines[47] == ":15: AttributeError"
+        assert tw_mock.lines[47] == ":15: AttributeError"
 
     @pytest.mark.parametrize("mode", ["from_none", "explicit_suppress"])
-    def test_exc_repr_chain_suppression(self, importasmod, mode):
+    def test_exc_repr_chain_suppression(self, importasmod, mode, tw_mock):
         """Check that exc repr does not show chained exceptions in Python 3.
         - When the exception is raised with "from None"
         - Explicitly suppressed with "chain=False" to ExceptionInfo.getrepr().
@@ -1226,24 +1190,23 @@ raise ValueError()
         )
         excinfo = pytest.raises(AttributeError, mod.f)
         r = excinfo.getrepr(style="long", chain=mode != "explicit_suppress")
-        tw = TWMock()
+        r.toterminal(tw_mock)
-        r.toterminal(tw)
+        for line in tw_mock.lines:
-        for line in tw.lines:
             print(line)
-        assert tw.lines[0] == ""
+        assert tw_mock.lines[0] == ""
-        assert tw.lines[1] == "    def f():"
+        assert tw_mock.lines[1] == "    def f():"
-        assert tw.lines[2] == "        try:"
+        assert tw_mock.lines[2] == "        try:"
-        assert tw.lines[3] == "            g()"
+        assert tw_mock.lines[3] == "            g()"
-        assert tw.lines[4] == "        except Exception:"
+        assert tw_mock.lines[4] == "        except Exception:"
-        assert tw.lines[5] == ">           raise AttributeError(){}".format(
+        assert tw_mock.lines[5] == ">           raise AttributeError(){}".format(
             raise_suffix
         )
-        assert tw.lines[6] == "E           AttributeError"
+        assert tw_mock.lines[6] == "E           AttributeError"
-        assert tw.lines[7] == ""
+        assert tw_mock.lines[7] == ""
-        line = tw.get_write_msg(8)
+        line = tw_mock.get_write_msg(8)
         assert line.endswith("mod.py")
-        assert tw.lines[9] == ":6: AttributeError"
+        assert tw_mock.lines[9] == ":6: AttributeError"
-        assert len(tw.lines) == 10
+        assert len(tw_mock.lines) == 10
 
     @pytest.mark.parametrize(
         "reason, description",
@@ -1304,7 +1267,7 @@ raise ValueError()
             ]
         )
 
-    def test_exc_chain_repr_cycle(self, importasmod):
+    def test_exc_chain_repr_cycle(self, importasmod, tw_mock):
         mod = importasmod(
             """
             class Err(Exception):
@@ -1325,9 +1288,8 @@ raise ValueError()
         )
         excinfo = pytest.raises(ZeroDivisionError, mod.unreraise)
         r = excinfo.getrepr(style="short")
-        tw = TWMock()
+        r.toterminal(tw_mock)
-        r.toterminal(tw)
+        out = "\n".join(line for line in tw_mock.lines if isinstance(line, str))
-        out = "\n".join(line for line in tw.lines if isinstance(line, str))
         expected_out = textwrap.dedent(
             """\
             :13: in unreraise

testing/conftest.py

@@ -55,3 +55,36 @@ def pytest_collection_modifyitems(config, items):
     items[:] = fast_items + neutral_items + slow_items + slowest_items
 
     yield
+
+
+@pytest.fixture
+def tw_mock():
+    """Returns a mock terminal writer"""
+
+    class TWMock:
+        WRITE = object()
+
+        def __init__(self):
+            self.lines = []
+            self.is_writing = False
+
+        def sep(self, sep, line=None):
+            self.lines.append((sep, line))
+
+        def write(self, msg, **kw):
+            self.lines.append((TWMock.WRITE, msg))
+
+        def line(self, line, **kw):
+            self.lines.append(line)
+
+        def markup(self, text, **kw):
+            return text
+
+        def get_write_msg(self, idx):
+            flag, msg = self.lines[idx]
+            assert flag == TWMock.WRITE
+            return msg
+
+        fullwidth = 80
+
+    return TWMock()

testing/test_reports.py

@@ -1,4 +1,5 @@
 import pytest
+from _pytest._code.code import ExceptionChainRepr
 from _pytest.pathlib import Path
 from _pytest.reports import CollectReport
 from _pytest.reports import TestReport
@@ -220,8 +221,8 @@ class TestReportSerialization:
         assert data["path1"] == str(testdir.tmpdir)
         assert data["path2"] == str(testdir.tmpdir)
 
-    def test_unserialization_failure(self, testdir):
+    def test_deserialization_failure(self, testdir):
-        """Check handling of failure during unserialization of report types."""
+        """Check handling of failure during deserialization of report types."""
         testdir.makepyfile(
             """
             def test_a():
@@ -242,6 +243,75 @@ class TestReportSerialization:
         ):
             TestReport._from_json(data)
 
+    @pytest.mark.parametrize("report_class", [TestReport, CollectReport])
+    def test_chained_exceptions(self, testdir, tw_mock, report_class):
+        """Check serialization/deserialization of report objects containing chained exceptions (#5786)"""
+        testdir.makepyfile(
+            """
+            def foo():
+                raise ValueError('value error')
+            def test_a():
+                try:
+                    foo()
+                except ValueError as e:
+                    raise RuntimeError('runtime error') from e
+            if {error_during_import}:
+                test_a()
+        """.format(
+                error_during_import=report_class is CollectReport
+            )
+        )
+
+        reprec = testdir.inline_run()
+        if report_class is TestReport:
+            reports = reprec.getreports("pytest_runtest_logreport")
+            # we have 3 reports: setup/call/teardown
+            assert len(reports) == 3
+            # get the call report
+            report = reports[1]
+        else:
+            assert report_class is CollectReport
+            # two collection reports: session and test file
+            reports = reprec.getreports("pytest_collectreport")
+            assert len(reports) == 2
+            report = reports[1]
+
+        def check_longrepr(longrepr):
+            """Check the attributes of the given longrepr object according to the test file.
+
+            We can get away with testing both CollectReport and TestReport with this function because
+            the longrepr objects are very similar.
+            """
+            assert isinstance(longrepr, ExceptionChainRepr)
+            assert longrepr.sections == [("title", "contents", "=")]
+            assert len(longrepr.chain) == 2
+            entry1, entry2 = longrepr.chain
+            tb1, fileloc1, desc1 = entry1
+            tb2, fileloc2, desc2 = entry2
+
+            assert "ValueError('value error')" in str(tb1)
+            assert "RuntimeError('runtime error')" in str(tb2)
+
+            assert (
+                desc1
+                == "The above exception was the direct cause of the following exception:"
+            )
+            assert desc2 is None
+
+        assert report.failed
+        assert len(report.sections) == 0
+        report.longrepr.addsection("title", "contents", "=")
+        check_longrepr(report.longrepr)
+
+        data = report._to_json()
+        loaded_report = report_class._from_json(data)
+        check_longrepr(loaded_report.longrepr)
+
+        # make sure we don't blow up on ``toterminal`` call; we don't test the actual output because it is very
+        # brittle and hard to maintain, but we can assume it is correct because ``toterminal`` is already tested
+        # elsewhere and we do check the contents of the longrepr object after loading it.
+        loaded_report.longrepr.toterminal(tw_mock)
+
 
 class TestHooks:
     """Test that the hooks are working correctly for plugins"""