Add pytest_report_serialize and pytest_report_unserialize hooks

These hooks will be used by pytest-xdist and pytest-subtests to
serialize and customize reports.

src/_pytest/config/__init__.py

@@ -140,6 +140,7 @@ default_plugins = (
     "stepwise",
     "warnings",
     "logging",
+    "reports",
 )
 
 

src/_pytest/hookspec.py

@@ -375,6 +375,41 @@ def pytest_runtest_logreport(report):
     the respective phase of executing a test. """
 
 
+@hookspec(firstresult=True)
+def pytest_report_serialize(config, report):
+    """
+    .. warning::
+        This hook is experimental and subject to change between pytest releases, even
+        bug fixes.
+
+        The intent is for this to be used by plugins maintained by the core-devs, such
+        as ``pytest-xdist``, ``pytest-subtests``, and as a replacement for the internal
+        'resultlog' plugin.
+
+        In the future it might become part of the public hook API.
+
+    Serializes the given report object into a data structure suitable for sending
+    over the wire, or converted to JSON.
+    """
+
+
+@hookspec(firstresult=True)
+def pytest_report_unserialize(config, data):
+    """
+    .. warning::
+        This hook is experimental and subject to change between pytest releases, even
+        bug fixes.
+
+        The intent is for this to be used by plugins maintained by the core-devs, such
+        as ``pytest-xdist``, ``pytest-subtests``, and as a replacement for the internal
+        'resultlog' plugin.
+
+        In the future it might become part of the public hook API.
+
+    Restores a report object previously serialized with pytest_report_serialize().;
+    """
+
+
 # -------------------------------------------------------------------------
 # Fixture related hooks
 # -------------------------------------------------------------------------

src/_pytest/reports.py

@@ -404,3 +404,19 @@ class CollectErrorRepr(TerminalRepr):
 
     def toterminal(self, out):
         out.line(self.longrepr, red=True)
+
+
+def pytest_report_serialize(report):
+    if isinstance(report, (TestReport, CollectReport)):
+        data = report._to_json()
+        data["_report_type"] = report.__class__.__name__
+        return data
+
+
+def pytest_report_unserialize(data):
+    if "_report_type" in data:
+        if data["_report_type"] == "TestReport":
+            return TestReport._from_json(data)
+        elif data["_report_type"] == "CollectReport":
+            return CollectReport._from_json(data)
+        assert "Unknown report_type unserialize data: {}".format(data["_report_type"])