TST: Add Sketch of unit tests for the new error handling

The sketched tests introduce test cases and explain the desired
behaviour.

unittests/test_error_handling.py

+# -*- encoding: utf-8 -*-
+#
+# ** header v3.0
+# This file is a part of the CaosDB Project.
+#
+# Copyright (C) 2020 Indiscale GmbH <info@indiscale.com>
+# Copyright (C) 2020 Florian Spreckelsen <f.spreckelsen@indiscale.com>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program. If not, see <https://www.gnu.org/licenses/>.
+#
+# ** end header
+#
+"""Test the new (as of June 2020) error handling. All errors should
+be TransactionErrors at first which may have one or more level of
+children.
+
+"""
+import caosdb as db
+from caosdb.common.models import raise_errors
+# TODO: Import the relevant error classes once they have been finalized.
+from caosdb.exceptions import (EntityDoesNotExistError,
+                               EntityHasNoDatatypeError,
+                               TransactionError)
+
+from pytest import raises
+
+
+# #################### Single Error Tests ####################
+
+
+def _add_error_message_to_entity(entity, code, description="Error message"):
+    """Attach error message with code and description to entity"""
+    message = db.Message(type="Error", code=code,
+                         description=description)
+    entity.add_message(message)
+
+    return enetity
+
+
+def test_has_no_datatype_error():
+    """Code 110; property without datatype"""
+    code = 110
+    prop = _add_error_message_to_entity(db.Property(name="TestProp"),
+                                        code)
+    with raises(TransactionError) as e:
+        raise_errors(prop)
+    # There should be exactly one child
+    assert len(e.errors) == 1
+    err = e.errors[0]
+    # check type and entity of only child
+    assert isinstance(err, EntityHasNoDatatypeError)
+    assert err.entity.name == prop.name
+
+
+def test_entity_does_not_exist_error():
+    """Code 101; entity does not exist"""
+    code = 101
+    ent = _add_error_message_to_entity(db.Entity(name="TestEnt"),
+                                       code)
+
+    db.Property(name="TestProp"),
+                                        code)
+    with raises(TransactionError) as e:
+        raise_errors(ent)
+    # There should be exactly one child
+    assert len(e.errors) == 1
+    err = e.errors[0]
+    # check type and entity of only child
+    assert isinstance(err, EntityDoesNotExistError)
+    assert err.entity.name == ent.name
+
+# TODO: remaining single error tests
+def test_entity_error():
+    """Code 0; most basic."""
+
+
+def test_unique_names_error():
+    """Code 152; name is not unique"""
+
+
+def test_authorization_exception():
+    """Code 403; transaction not allowed"""
+
+
+# #################### Children with children ####################
+
+
+def test_unqualified_parents_error():
+    """Code 116; parent does not exist"""
+    code = 116
+    entity_does_not_exist_code = 101
+    parent = _add_error_message_to_entity(
+        db.RecordType(name="TestParent"),
+        entity_does_not_exist_code)
+    rec = _add_error_message_to_entity(db.Record(name="TestRecord"),
+                                       code)
+    rec.add_parent(parent)
+    with raises(TransactionError) as e:
+        raise_errors(rec)
+    # TODO: Both direct and indirect children should be in the errors
+    # list, the only direct child is the UnqualifiedParentsError with
+    # entity rec and one child of its own; the EntityDoesNotExistError
+    # with entity parent.
+
+
+def test_unqualified_properties_error():
+    """Code 114; properties do not exist or have wrong data types or
+    values.
+
+    """
+    code = 114
+    # TODO: One record with two properties; one doesn't exist (code
+    # 101), the other has a wrong value (EntityError, code 0). Then
+    # check whether all levels are in order.
+
+
+# #################### Multiple errors ####################
+
+
+def test_parent_and_properties_errors():
+    """Record with UnqualifiedParentsError and UnqualifiedPropertiesError,
+    and corresponding parent and properties with their errors as
+    above. Test whether all levels are in order.
+
+    """
+    # TODO: record with code 114 and 116, properties with 101 and 0,
+    # parent with 101
+
+
+def test_container_with_faulty_elements():
+    """Container with valid and invalid entities. All faulty entities have
+    to be reflected correctly in the errors list of the
+    TransactionError raised by the container.
+
+    """