diff --git a/tests/unit/config/sort_services_test.py b/tests/unit/config/sort_services_test.py
index 3279ece490..f59906644a 100644
--- a/tests/unit/config/sort_services_test.py
+++ b/tests/unit/config/sort_services_test.py
@@ -6,10 +6,9 @@ import pytest
 from compose.config.errors import DependencyError
 from compose.config.sort_services import sort_service_dicts
 from compose.config.types import VolumeFromSpec
-from tests import unittest
 
 
-class SortServiceTest(unittest.TestCase):
+class TestSortService(object):
     def test_sort_service_dicts_1(self):
         services = [
             {
@@ -25,10 +24,10 @@ class SortServiceTest(unittest.TestCase):
         ]
 
         sorted_services = sort_service_dicts(services)
-        self.assertEqual(len(sorted_services), 3)
-        self.assertEqual(sorted_services[0]['name'], 'grunt')
-        self.assertEqual(sorted_services[1]['name'], 'redis')
-        self.assertEqual(sorted_services[2]['name'], 'web')
+        assert len(sorted_services) == 3
+        assert sorted_services[0]['name'] == 'grunt'
+        assert sorted_services[1]['name'] == 'redis'
+        assert sorted_services[2]['name'] == 'web'
 
     def test_sort_service_dicts_2(self):
         services = [
@@ -46,10 +45,10 @@ class SortServiceTest(unittest.TestCase):
         ]
 
         sorted_services = sort_service_dicts(services)
-        self.assertEqual(len(sorted_services), 3)
-        self.assertEqual(sorted_services[0]['name'], 'redis')
-        self.assertEqual(sorted_services[1]['name'], 'postgres')
-        self.assertEqual(sorted_services[2]['name'], 'web')
+        assert len(sorted_services) == 3
+        assert sorted_services[0]['name'] == 'redis'
+        assert sorted_services[1]['name'] == 'postgres'
+        assert sorted_services[2]['name'] == 'web'
 
     def test_sort_service_dicts_3(self):
         services = [
@@ -67,10 +66,10 @@ class SortServiceTest(unittest.TestCase):
         ]
 
         sorted_services = sort_service_dicts(services)
-        self.assertEqual(len(sorted_services), 3)
-        self.assertEqual(sorted_services[0]['name'], 'child')
-        self.assertEqual(sorted_services[1]['name'], 'parent')
-        self.assertEqual(sorted_services[2]['name'], 'grandparent')
+        assert len(sorted_services) == 3
+        assert sorted_services[0]['name'] == 'child'
+        assert sorted_services[1]['name'] == 'parent'
+        assert sorted_services[2]['name'] == 'grandparent'
 
     def test_sort_service_dicts_4(self):
         services = [
@@ -88,10 +87,10 @@ class SortServiceTest(unittest.TestCase):
         ]
 
         sorted_services = sort_service_dicts(services)
-        self.assertEqual(len(sorted_services), 3)
-        self.assertEqual(sorted_services[0]['name'], 'child')
-        self.assertEqual(sorted_services[1]['name'], 'parent')
-        self.assertEqual(sorted_services[2]['name'], 'grandparent')
+        assert len(sorted_services) == 3
+        assert sorted_services[0]['name'] == 'child'
+        assert sorted_services[1]['name'] == 'parent'
+        assert sorted_services[2]['name'] == 'grandparent'
 
     def test_sort_service_dicts_5(self):
         services = [
@@ -109,10 +108,10 @@ class SortServiceTest(unittest.TestCase):
         ]
 
         sorted_services = sort_service_dicts(services)
-        self.assertEqual(len(sorted_services), 3)
-        self.assertEqual(sorted_services[0]['name'], 'child')
-        self.assertEqual(sorted_services[1]['name'], 'parent')
-        self.assertEqual(sorted_services[2]['name'], 'grandparent')
+        assert len(sorted_services) == 3
+        assert sorted_services[0]['name'] == 'child'
+        assert sorted_services[1]['name'] == 'parent'
+        assert sorted_services[2]['name'] == 'grandparent'
 
     def test_sort_service_dicts_6(self):
         services = [
@@ -130,10 +129,10 @@ class SortServiceTest(unittest.TestCase):
         ]
 
         sorted_services = sort_service_dicts(services)
-        self.assertEqual(len(sorted_services), 3)
-        self.assertEqual(sorted_services[0]['name'], 'child')
-        self.assertEqual(sorted_services[1]['name'], 'parent')
-        self.assertEqual(sorted_services[2]['name'], 'grandparent')
+        assert len(sorted_services) == 3
+        assert sorted_services[0]['name'] == 'child'
+        assert sorted_services[1]['name'] == 'parent'
+        assert sorted_services[2]['name'] == 'grandparent'
 
     def test_sort_service_dicts_7(self):
         services = [
@@ -155,11 +154,11 @@ class SortServiceTest(unittest.TestCase):
         ]
 
         sorted_services = sort_service_dicts(services)
-        self.assertEqual(len(sorted_services), 4)
-        self.assertEqual(sorted_services[0]['name'], 'one')
-        self.assertEqual(sorted_services[1]['name'], 'two')
-        self.assertEqual(sorted_services[2]['name'], 'three')
-        self.assertEqual(sorted_services[3]['name'], 'four')
+        assert len(sorted_services) == 4
+        assert sorted_services[0]['name'] == 'one'
+        assert sorted_services[1]['name'] == 'two'
+        assert sorted_services[2]['name'] == 'three'
+        assert sorted_services[3]['name'] == 'four'
 
     def test_sort_service_dicts_circular_imports(self):
         services = [
@@ -173,13 +172,10 @@ class SortServiceTest(unittest.TestCase):
             },
         ]
 
-        try:
+        with pytest.raises(DependencyError) as exc:
             sort_service_dicts(services)
-        except DependencyError as e:
-            self.assertIn('redis', e.msg)
-            self.assertIn('web', e.msg)
-        else:
-            self.fail('Should have thrown an DependencyError')
+        assert 'redis' in exc.exconly()
+        assert 'web' in exc.exconly()
 
     def test_sort_service_dicts_circular_imports_2(self):
         services = [
@@ -196,13 +192,10 @@ class SortServiceTest(unittest.TestCase):
             }
         ]
 
-        try:
+        with pytest.raises(DependencyError) as exc:
             sort_service_dicts(services)
-        except DependencyError as e:
-            self.assertIn('redis', e.msg)
-            self.assertIn('web', e.msg)
-        else:
-            self.fail('Should have thrown an DependencyError')
+        assert 'redis' in exc.exconly()
+        assert 'web' in exc.exconly()
 
     def test_sort_service_dicts_circular_imports_3(self):
         services = [
@@ -220,13 +213,10 @@ class SortServiceTest(unittest.TestCase):
             }
         ]
 
-        try:
+        with pytest.raises(DependencyError) as exc:
             sort_service_dicts(services)
-        except DependencyError as e:
-            self.assertIn('a', e.msg)
-            self.assertIn('b', e.msg)
-        else:
-            self.fail('Should have thrown an DependencyError')
+        assert 'a' in exc.exconly()
+        assert 'b' in exc.exconly()
 
     def test_sort_service_dicts_self_imports(self):
         services = [
@@ -236,12 +226,9 @@ class SortServiceTest(unittest.TestCase):
             },
         ]
 
-        try:
+        with pytest.raises(DependencyError) as exc:
             sort_service_dicts(services)
-        except DependencyError as e:
-            self.assertIn('web', e.msg)
-        else:
-            self.fail('Should have thrown an DependencyError')
+        assert 'web' in exc.exconly()
 
     def test_sort_service_dicts_depends_on_self(self):
         services = [