Tests: switched to using f-strings.

Previously, it was necessary to support older versions of Python for
compatibility.  F-strings were released in Python 3.6.  Python 3.5 was
marked as unsupported by the end of 2020, so now it's possible to start
using f-strings safely for better readability and performance.

17 files changed, 127 insertions, 137 deletions

diff --git a/test/unit/applications/lang/go.py b/test/unit/applications/lang/go.py
index 14e76362..557753a4 100644
--- a/test/unit/applications/lang/go.py
+++ b/test/unit/applications/lang/go.py
@@ -14,23 +14,21 @@ class TestApplicationGo(TestApplicationProto):
         except subprocess.CalledProcessError:
             return None
 
-        temp_dir = option.temp_dir + '/go/'
+        temp_dir = f'{option.temp_dir}/go/'
 
         if not os.path.exists(temp_dir):
             os.mkdir(temp_dir)
 
-        cache_dir = option.cache_dir + '/go-build'
+        cache_dir = f'{option.cache_dir}/go-build'
 
         if not os.path.exists(cache_dir):
             os.mkdir(cache_dir)
 
         env = os.environ.copy()
-        env['GOPATH'] = option.current_dir + '/build/go'
+        env['GOPATH'] = f'{option.current_dir}/build/go'
         env['GOCACHE'] = cache_dir
 
-        shutil.copy2(
-            option.test_dir + '/go/' + script + '/' + name + '.go', temp_dir
-        )
+        shutil.copy2(f'{option.test_dir}/go/{script}/{name}.go', temp_dir)
 
         if static:
             args = [
@@ -41,21 +39,21 @@ class TestApplicationGo(TestApplicationProto):
                 '-ldflags',
                 '-extldflags "-static"',
                 '-o',
-                temp_dir + name,
-                temp_dir + name + '.go',
+                f'{temp_dir}{name}',
+                f'{temp_dir}{name}.go',
             ]
         else:
             args = [
                 'go',
                 'build',
                 '-o',
-                temp_dir + name,
-                temp_dir + name + '.go',
+                f'{temp_dir}{name}',
+                f'{temp_dir}{name}.go',
             ]
 
-        replace_path = option.current_dir + '/build/go/src/unit.nginx.org/go'
+        replace_path = f'{option.current_dir}/build/go/src/unit.nginx.org/go'
 
-        with open(temp_dir + 'go.mod', 'w') as f:
+        with open(f'{temp_dir}go.mod', 'w') as f:
             f.write(
                 f"""module test/app
 require unit.nginx.org/go v0.0.0
@@ -64,7 +62,7 @@ replace unit.nginx.org/go => {replace_path}
             )
 
         if option.detailed:
-            print("\n$ GOPATH=" + env['GOPATH'] + " " + " ".join(args))
+            print(f'\n$ GOPATH={env["GOPATH"]} {" ".join(args)}')
 
         try:
             output = subprocess.check_output(
@@ -82,18 +80,18 @@ replace unit.nginx.org/go => {replace_path}
     def load(self, script, name='app', **kwargs):
         static_build = False
 
-        wdir = option.test_dir + "/go/" + script
-        executable = option.temp_dir + "/go/" + name
+        wdir = f'{option.test_dir}/go/{script}'
+        executable = f'{option.temp_dir}/go/{name}'
 
         if 'isolation' in kwargs and 'rootfs' in kwargs['isolation']:
             wdir = "/go/"
-            executable = "/go/" + name
+            executable = f"/go/{name}"
             static_build = True
 
         TestApplicationGo.prepare_env(script, name, static=static_build)
 
         conf = {
-            "listeners": {"*:7080": {"pass": "applications/" + script}},
+            "listeners": {"*:7080": {"pass": f"applications/{script}"}},
             "applications": {
                 script: {
                     "type": "external",
diff --git a/test/unit/applications/lang/java.py b/test/unit/applications/lang/java.py
index c8936274..cd955974 100644
--- a/test/unit/applications/lang/java.py
+++ b/test/unit/applications/lang/java.py
@@ -12,10 +12,10 @@ class TestApplicationJava(TestApplicationProto):
     application_type = "java"
 
     def prepare_env(self, script):
-        app_path = option.temp_dir + '/java'
-        web_inf_path = app_path + '/WEB-INF/'
-        classes_path = web_inf_path + 'classes/'
-        script_path = option.test_dir + '/java/' + script + '/'
+        app_path = f'{option.temp_dir}/java'
+        web_inf_path = f'{app_path}/WEB-INF/'
+        classes_path = f'{web_inf_path}classes/'
+        script_path = f'{option.test_dir}/java/{script}/'
 
         if not os.path.isdir(app_path):
             os.makedirs(app_path)
@@ -23,7 +23,7 @@ class TestApplicationJava(TestApplicationProto):
         src = []
 
         for f in os.listdir(script_path):
-            file_path = script_path + f
+            file_path = f'{script_path}{f}'
 
             if f.endswith('.java'):
                 src.append(file_path)
@@ -36,7 +36,7 @@ class TestApplicationJava(TestApplicationProto):
                 if f == 'WEB-INF':
                     continue
 
-                shutil.copytree(file_path, app_path + '/' + f)
+                shutil.copytree(file_path, f'{app_path}/{f}')
                 continue
 
             if f == 'web.xml':
@@ -52,11 +52,11 @@ class TestApplicationJava(TestApplicationProto):
                 os.makedirs(classes_path)
 
             classpath = (
-                option.current_dir + '/build/tomcat-servlet-api-9.0.70.jar'
+                f'{option.current_dir}/build/tomcat-servlet-api-9.0.70.jar'
             )
 
             ws_jars = glob.glob(
-                option.current_dir + '/build/websocket-api-java-*.jar'
+                f'{option.current_dir}/build/websocket-api-java-*.jar'
             )
 
             if not ws_jars:
@@ -74,12 +74,12 @@ class TestApplicationJava(TestApplicationProto):
                 '-d',
                 classes_path,
                 '-classpath',
-                classpath + ':' + ws_jars[0],
+                f'{classpath}:{ws_jars[0]}',
             ]
             javac.extend(src)
 
             if option.detailed:
-                print("\n$ " + " ".join(javac))
+                print(f'\n$ {" ".join(javac)}')
 
             try:
                 subprocess.check_output(javac, stderr=subprocess.STDOUT)
@@ -88,26 +88,24 @@ class TestApplicationJava(TestApplicationProto):
                 raise
 
             except subprocess.CalledProcessError:
-                pytest.fail('Can\'t run javac process.')
+                pytest.fail("Can't run javac process.")
 
     def load(self, script, **kwargs):
         self.prepare_env(script)
 
+        script_path = f'{option.test_dir}/java/{script}/'
         self._load_conf(
             {
-                "listeners": {"*:7080": {"pass": "applications/" + script}},
+                "listeners": {"*:7080": {"pass": f"applications/{script}"}},
                 "applications": {
                     script: {
-                        "unit_jars": option.current_dir + '/build',
+                        "unit_jars": f'{option.current_dir}/build',
                         "type": self.get_application_type(),
                         "processes": {"spare": 0},
-                        "working_directory": option.test_dir
-                        + '/java/'
-                        + script
-                        + '/',
-                        "webapp": option.temp_dir + '/java',
+                        "working_directory": script_path,
+                        "webapp": f'{option.temp_dir}/java',
                     }
                 },
             },
-            **kwargs
+            **kwargs,
         )
diff --git a/test/unit/applications/lang/node.py b/test/unit/applications/lang/node.py
index 5d05c70c..87d5a19c 100644
--- a/test/unit/applications/lang/node.py
+++ b/test/unit/applications/lang/node.py
@@ -13,16 +13,16 @@ class TestApplicationNode(TestApplicationProto):
     def prepare_env(self, script):
         # copy application
         shutil.copytree(
-            option.test_dir + '/node/' + script, option.temp_dir + '/node'
+            f'{option.test_dir}/node/{script}', f'{option.temp_dir}/node'
         )
 
         # copy modules
         shutil.copytree(
-            option.current_dir + '/node/node_modules',
-            option.temp_dir + '/node/node_modules',
+            f'{option.current_dir}/node/node_modules',
+            f'{option.temp_dir}/node/node_modules',
         )
 
-        public_dir(option.temp_dir + '/node')
+        public_dir(f'{option.temp_dir}/node')
 
     def load(self, script, name='app.js', **kwargs):
         self.prepare_env(script)
@@ -43,17 +43,17 @@ class TestApplicationNode(TestApplicationProto):
         self._load_conf(
             {
                 "listeners": {
-                    "*:7080": {"pass": "applications/" + quote(script, '')}
+                    "*:7080": {"pass": f"applications/{quote(script, '')}"}
                 },
                 "applications": {
                     script: {
                         "type": "external",
                         "processes": {"spare": 0},
-                        "working_directory": option.temp_dir + '/node',
+                        "working_directory": f'{option.temp_dir}/node',
                         "executable": '/usr/bin/env',
                         "arguments": arguments,
                     }
                 },
             },
-            **kwargs
+            **kwargs,
         )
diff --git a/test/unit/applications/lang/perl.py b/test/unit/applications/lang/perl.py
index 58b867f0..19852363 100644
--- a/test/unit/applications/lang/perl.py
+++ b/test/unit/applications/lang/perl.py
@@ -6,19 +6,19 @@ class TestApplicationPerl(TestApplicationProto):
     application_type = "perl"
 
     def load(self, script, name='psgi.pl', **kwargs):
-        script_path = option.test_dir + '/perl/' + script
+        script_path = f'{option.test_dir}/perl/{script}'
 
         self._load_conf(
             {
-                "listeners": {"*:7080": {"pass": "applications/" + script}},
+                "listeners": {"*:7080": {"pass": f"applications/{script}"}},
                 "applications": {
                     script: {
                         "type": self.get_application_type(),
                         "processes": {"spare": 0},
                         "working_directory": script_path,
-                        "script": script_path + '/' + name,
+                        "script": f'{script_path}/{name}',
                     }
                 },
             },
-            **kwargs
+            **kwargs,
         )
diff --git a/test/unit/applications/lang/php.py b/test/unit/applications/lang/php.py
index 5319d2ca..1b94c3ae 100644
--- a/test/unit/applications/lang/php.py
+++ b/test/unit/applications/lang/php.py
@@ -9,18 +9,18 @@ class TestApplicationPHP(TestApplicationProto):
     application_type = "php"
 
     def load(self, script, index='index.php', **kwargs):
-        script_path = option.test_dir + '/php/' + script
+        script_path = f'{option.test_dir}/php/{script}'
 
         if kwargs.get('isolation') and kwargs['isolation'].get('rootfs'):
             rootfs = kwargs['isolation']['rootfs']
 
-            if not os.path.exists(rootfs + '/app/php/'):
-                os.makedirs(rootfs + '/app/php/')
+            if not os.path.exists(f'{rootfs}/app/php/'):
+                os.makedirs(f'{rootfs}/app/php/')
 
-            if not os.path.exists(rootfs + '/app/php/' + script):
-                shutil.copytree(script_path, rootfs + '/app/php/' + script)
+            if not os.path.exists(f'{rootfs}/app/php/{script}'):
+                shutil.copytree(script_path, f'{rootfs}/app/php/{script}')
 
-            script_path = '/app/php/' + script
+            script_path = f'/app/php/{script}'
 
         app = {
             "type": self.get_application_type(),
@@ -41,8 +41,8 @@ class TestApplicationPHP(TestApplicationProto):
 
         self._load_conf(
             {
-                "listeners": {"*:7080": {"pass": "applications/" + script}},
+                "listeners": {"*:7080": {"pass": f"applications/{script}"}},
                 "applications": {script: app},
             },
-            **kwargs
+            **kwargs,
         )
diff --git a/test/unit/applications/lang/python.py b/test/unit/applications/lang/python.py
index 3768cf07..0bb69992 100644
--- a/test/unit/applications/lang/python.py
+++ b/test/unit/applications/lang/python.py
@@ -20,18 +20,18 @@ class TestApplicationPython(TestApplicationProto):
         if script[0] == '/':
             script_path = script
         else:
-            script_path = option.test_dir + '/python/' + script
+            script_path = f'{option.test_dir}/python/{script}'
 
         if kwargs.get('isolation') and kwargs['isolation'].get('rootfs'):
             rootfs = kwargs['isolation']['rootfs']
 
-            if not os.path.exists(rootfs + '/app/python/'):
-                os.makedirs(rootfs + '/app/python/')
+            if not os.path.exists(f'{rootfs}/app/python/'):
+                os.makedirs(f'{rootfs}/app/python/')
 
-            if not os.path.exists(rootfs + '/app/python/' + name):
-                shutil.copytree(script_path, rootfs + '/app/python/' + name)
+            if not os.path.exists(f'{rootfs}/app/python/{name}'):
+                shutil.copytree(script_path, f'{rootfs}/app/python/{name}')
 
-            script_path = '/app/python/' + name
+            script_path = f'/app/python/{name}'
 
         app = {
             "type": self.get_application_type(),
@@ -58,9 +58,9 @@ class TestApplicationPython(TestApplicationProto):
         self._load_conf(
             {
                 "listeners": {
-                    "*:7080": {"pass": "applications/" + quote(name, '')}
+                    "*:7080": {"pass": f"applications/{quote(name, '')}"}
                 },
                 "applications": {name: app},
             },
-            **kwargs
+            **kwargs,
         )
diff --git a/test/unit/applications/lang/ruby.py b/test/unit/applications/lang/ruby.py
index 824bfe7f..e0712fc6 100644
--- a/test/unit/applications/lang/ruby.py
+++ b/test/unit/applications/lang/ruby.py
@@ -10,22 +10,22 @@ class TestApplicationRuby(TestApplicationProto):
 
     def prepare_env(self, script):
         shutil.copytree(
-            option.test_dir + '/ruby/' + script,
-            option.temp_dir + '/ruby/' + script,
+            f'{option.test_dir}/ruby/{script}',
+            f'{option.temp_dir}/ruby/{script}',
         )
 
-        public_dir(option.temp_dir + '/ruby/' + script)
+        public_dir(f'{option.temp_dir}/ruby/{script}')
 
     def load(self, script, name='config.ru', **kwargs):
         self.prepare_env(script)
 
-        script_path = option.temp_dir + '/ruby/' + script
+        script_path = f'{option.temp_dir}/ruby/{script}'
 
         app = {
             "type": self.get_application_type(),
             "processes": {"spare": 0},
             "working_directory": script_path,
-            "script": script_path + '/' + name,
+            "script": f'{script_path}/{name}',
         }
 
         for key in [
@@ -36,8 +36,8 @@ class TestApplicationRuby(TestApplicationProto):
 
         self._load_conf(
             {
-                "listeners": {"*:7080": {"pass": "applications/" + script}},
+                "listeners": {"*:7080": {"pass": f"applications/{script}"}},
                 "applications": {script: app},
             },
-            **kwargs
+            **kwargs,
         )
diff --git a/test/unit/applications/tls.py b/test/unit/applications/tls.py
index 63f0c9c4..e5813312 100644
--- a/test/unit/applications/tls.py
+++ b/test/unit/applications/tls.py
@@ -22,13 +22,13 @@ class TestApplicationTLS(TestApplicationProto):
                 '-x509',
                 '-new',
                 '-subj',
-                '/CN=' + name + '/',
+                f'/CN={name}/',
                 '-config',
-                option.temp_dir + '/openssl.conf',
+                f'{option.temp_dir}/openssl.conf',
                 '-out',
-                option.temp_dir + '/' + name + '.crt',
+                f'{option.temp_dir}/{name}.crt',
                 '-keyout',
-                option.temp_dir + '/' + name + '.key',
+                f'{option.temp_dir}/{name}.key',
             ],
             stderr=subprocess.STDOUT,
         )
@@ -40,11 +40,11 @@ class TestApplicationTLS(TestApplicationProto):
         if key is None:
             key = crt
 
-        key_path = option.temp_dir + '/' + key + '.key'
-        crt_path = option.temp_dir + '/' + crt + '.crt'
+        key_path = f'{option.temp_dir}/{key}.key'
+        crt_path = f'{option.temp_dir}/{crt}.crt'
 
         with open(key_path, 'rb') as k, open(crt_path, 'rb') as c:
-            return self.conf(k.read() + c.read(), '/certificates/' + crt)
+            return self.conf(k.read() + c.read(), f'/certificates/{crt}')
 
     def get_ssl(self, **kwargs):
         return self.get(wrapper=self.context.wrap_socket, **kwargs)
@@ -54,54 +54,48 @@ class TestApplicationTLS(TestApplicationProto):
 
     def openssl_conf(self, rewrite=False, alt_names=None):
         alt_names = alt_names or []
-
-        conf_path = option.temp_dir + '/openssl.conf'
+        conf_path = f'{option.temp_dir}/openssl.conf'
 
         if not rewrite and os.path.exists(conf_path):
             return
 
         # Generates alt_names section with dns names
-        a_names = "[alt_names]\n"
+        a_names = '[alt_names]\n'
         for i, k in enumerate(alt_names, 1):
             k = k.split('|')
 
             if k[0] == 'IP':
-                a_names += "IP.%d = %s\n" % (i, k[1])
+                a_names += f'IP.{i} = {k[1]}\n'
             else:
-                a_names += "DNS.%d = %s\n" % (i, k[0])
+                a_names += f'DNS.{i} = {k[0]}\n'
 
         # Generates section for sign request extension
-        a_sec = """req_extensions = myca_req_extensions
+        a_sec = f'''req_extensions = myca_req_extensions
 
 [ myca_req_extensions ]
 subjectAltName = @alt_names
 
-{a_names}""".format(
-            a_names=a_names
-        )
+{a_names}'''
 
         with open(conf_path, 'w') as f:
             f.write(
-                """[ req ]
+                f'''[ req ]
 default_bits = 2048
 encrypt_key = no
 distinguished_name = req_distinguished_name
 
-{a_sec}
-[ req_distinguished_name ]""".format(
-                    a_sec=a_sec if alt_names else ""
-                )
+{a_sec if alt_names else ""}
+[ req_distinguished_name ]'''
             )
 
     def load(self, script, name=None):
         if name is None:
             name = script
 
-        script_path = option.test_dir + '/python/' + script
-
+        script_path = f'{option.test_dir}/python/{script}'
         self._load_conf(
             {
-                "listeners": {"*:7080": {"pass": "applications/" + name}},
+                "listeners": {"*:7080": {"pass": f"applications/{name}"}},
                 "applications": {
                     name: {
                         "type": "python",
diff --git a/test/unit/applications/websockets.py b/test/unit/applications/websockets.py
index 15f212ff..a4b9287d 100644
--- a/test/unit/applications/websockets.py
+++ b/test/unit/applications/websockets.py
@@ -52,7 +52,7 @@ class TestApplicationWebsocket(TestApplicationProto):
         while True:
             rlist = select.select([sock], [], [], 60)[0]
             if not rlist:
-                pytest.fail('Can\'t read response from server.')
+                pytest.fail("Can't read response from server.")
 
             resp += sock.recv(4096).decode()
 
@@ -77,7 +77,7 @@ class TestApplicationWebsocket(TestApplicationProto):
                     # For all current cases if the "read_timeout" was changed
                     # than test do not expect to get a response from server.
                     if read_timeout == 60:
-                        pytest.fail('Can\'t read response from server.')
+                        pytest.fail("Can't read response from server.")
                     break
 
                 data += sock.recv(bytes - len(data))
diff --git a/test/unit/check/chroot.py b/test/unit/check/chroot.py
index 40b75058..1b7aae90 100644
--- a/test/unit/check/chroot.py
+++ b/test/unit/check/chroot.py
@@ -12,7 +12,7 @@ def check_chroot():
     resp = http.put(
         url='/config',
         sock_type='unix',
-        addr=option.temp_dir + '/control.unit.sock',
+        addr=f'{option.temp_dir}/control.unit.sock',
         body=json.dumps(
             {
                 "listeners": {"*:7080": {"pass": "routes"}},
diff --git a/test/unit/check/isolation.py b/test/unit/check/isolation.py
index 9bd835a3..4ebce893 100644
--- a/test/unit/check/isolation.py
+++ b/test/unit/check/isolation.py
@@ -27,8 +27,8 @@ def check_isolation():
                 "empty": {
                     "type": "external",
                     "processes": {"spare": 0},
-                    "working_directory": option.test_dir + "/go/empty",
-                    "executable": option.temp_dir + "/go/app",
+                    "working_directory": f"{option.test_dir}/go/empty",
+                    "executable": f"{option.test_dir}/go/app",
                     "isolation": {"namespaces": {"credential": True}},
                 },
             },
@@ -41,8 +41,8 @@ def check_isolation():
                 "empty": {
                     "type": "python",
                     "processes": {"spare": 0},
-                    "path": option.test_dir + "/python/empty",
-                    "working_directory": option.test_dir + "/python/empty",
+                    "path": f"{option.test_dir}/python/empty",
+                    "working_directory": f"{option.test_dir}/python/empty",
                     "module": "wsgi",
                     "isolation": {"namespaces": {"credential": True}},
                 }
@@ -56,8 +56,8 @@ def check_isolation():
                 "phpinfo": {
                     "type": "php",
                     "processes": {"spare": 0},
-                    "root": option.test_dir + "/php/phpinfo",
-                    "working_directory": option.test_dir + "/php/phpinfo",
+                    "root": f"{option.test_dir}/php/phpinfo",
+                    "working_directory": f"{option.test_dir}/php/phpinfo",
                     "index": "index.php",
                     "isolation": {"namespaces": {"credential": True}},
                 }
@@ -73,8 +73,8 @@ def check_isolation():
                 "empty": {
                     "type": "ruby",
                     "processes": {"spare": 0},
-                    "working_directory": option.temp_dir + "/ruby/empty",
-                    "script": option.temp_dir + "/ruby/empty/config.ru",
+                    "working_directory": f"{option.temp_dir}/ruby/empty",
+                    "script": f"{option.temp_dir}/ruby/empty/config.ru",
                     "isolation": {"namespaces": {"credential": True}},
                 }
             },
@@ -87,11 +87,11 @@ def check_isolation():
             "listeners": {"*:7080": {"pass": "applications/empty"}},
             "applications": {
                 "empty": {
-                    "unit_jars": option.current_dir + "/build",
+                    "unit_jars": f"{option.current_dir}/build",
                     "type": "java",
                     "processes": {"spare": 0},
-                    "working_directory": option.test_dir + "/java/empty/",
-                    "webapp": option.temp_dir + "/java",
+                    "working_directory": f"{option.temp_dir}/java/empty/",
+                    "webapp": f"{option.temp_dir}/java",
                     "isolation": {"namespaces": {"credential": True}},
                 }
             },
@@ -106,7 +106,7 @@ def check_isolation():
                 "basic": {
                     "type": "external",
                     "processes": {"spare": 0},
-                    "working_directory": option.temp_dir + "/node",
+                    "working_directory": f"{option.temp_dir}/node",
                     "executable": "app.js",
                     "isolation": {"namespaces": {"credential": True}},
                 }
@@ -120,8 +120,8 @@ def check_isolation():
                 "body_empty": {
                     "type": "perl",
                     "processes": {"spare": 0},
-                    "working_directory": option.test_dir + "/perl/body_empty",
-                    "script": option.test_dir + "/perl/body_empty/psgi.pl",
+                    "working_directory": f"{option.test_dir}/perl/body_empty",
+                    "script": f"{option.test_dir}/perl/body_empty/psgi.pl",
                     "isolation": {"namespaces": {"credential": True}},
                 }
             },
@@ -133,7 +133,7 @@ def check_isolation():
     resp = http.put(
         url='/config',
         sock_type='unix',
-        addr=option.temp_dir + '/control.unit.sock',
+        addr=f'{option.temp_dir}/control.unit.sock',
         body=json.dumps(conf),
     )
 
diff --git a/test/unit/check/node.py b/test/unit/check/node.py
index e053a749..dd59e7a4 100644
--- a/test/unit/check/node.py
+++ b/test/unit/check/node.py
@@ -3,7 +3,7 @@ import subprocess
 
 
 def check_node(current_dir):
-    if not os.path.exists(current_dir + '/node/node_modules'):
+    if not os.path.exists(f'{current_dir}/node/node_modules'):
         return None
 
     try:
diff --git a/test/unit/check/unix_abstract.py b/test/unit/check/unix_abstract.py
index 5d1f629e..aadde43a 100644
--- a/test/unit/check/unix_abstract.py
+++ b/test/unit/check/unix_abstract.py
@@ -12,7 +12,7 @@ def check_unix_abstract():
     resp = http.put(
         url='/config',
         sock_type='unix',
-        addr=option.temp_dir + '/control.unit.sock',
+        addr=f'{option.temp_dir}/control.unit.sock',
         body=json.dumps(
             {
                 "listeners": {"unix:@sock": {"pass": "routes"}},
diff --git a/test/unit/control.py b/test/unit/control.py
index 99436ca0..61b6edf4 100644
--- a/test/unit/control.py
+++ b/test/unit/control.py
@@ -21,7 +21,7 @@ def args_handler(conf_func):
 
             url = args[1] if len(args) == 2 else url_default
 
-        url = url if url.startswith('/') else url_default + '/' + url
+        url = url if url.startswith('/') else f'{url_default}/{url}'
         arguments = (self, url) if conf is None else (self, conf, url)
 
         return json.loads(conf_func(*arguments))
@@ -50,7 +50,7 @@ class TestControl(TestHTTP):
         args = {
             'url': url,
             'sock_type': 'unix',
-            'addr': option.temp_dir + '/control.unit.sock',
+            'addr': f'{option.temp_dir}/control.unit.sock',
         }
 
         if conf is not None:
diff --git a/test/unit/http.py b/test/unit/http.py
index c48a720f..6a267e26 100644
--- a/test/unit/http.py
+++ b/test/unit/http.py
@@ -53,13 +53,13 @@ class TestHTTP:
                 sock.connect(connect_args)
             except (ConnectionRefusedError, FileNotFoundError):
                 sock.close()
-                pytest.fail('Client can\'t connect to the server.')
+                pytest.fail("Client can't connect to the server.")
 
         else:
             sock = kwargs['sock']
 
         if 'raw' not in kwargs:
-            req = ' '.join([start_str, url, http]) + crlf
+            req = f'{start_str} {url} {http}{crlf}'
 
             if body != b'':
                 if isinstance(body, str):
@@ -75,10 +75,10 @@ class TestHTTP:
             for header, value in headers.items():
                 if isinstance(value, list):
                     for v in value:
-                        req += header + ': ' + str(v) + crlf
+                        req += f'{header}: {v}{crlf}'
 
                 else:
-                    req += header + ': ' + str(value) + crlf
+                    req += f'{header}: {value}{crlf}'
 
             req = (req + crlf).encode() + body
 
@@ -151,12 +151,12 @@ class TestHTTP:
         len_log = len(log)
         if len_log > limit:
             log = log[:limit]
-            appendix = '(...logged %s of %s bytes)' % (limit, len_log)
+            appendix = f'(...logged {limit} of {len_log} bytes)'
 
             if isinstance(log, bytes):
                 appendix = appendix.encode()
 
-            log = log + appendix
+            log = f'{log}{appendix}'
 
         return log
 
@@ -188,7 +188,7 @@ class TestHTTP:
                 # For all current cases if the "read_timeout" was changed
                 # than test do not expect to get a response from server.
                 if timeout == timeout_default:
-                    pytest.fail('Can\'t read response from server.')
+                    pytest.fail("Can't read response from server.")
                 break
 
             try:
@@ -263,7 +263,7 @@ class TestHTTP:
                 size = int(chunks.pop(0), 16)
 
             except ValueError:
-                pytest.fail('Invalid chunk size %s' % str(size))
+                pytest.fail(f'Invalid chunk size {size}')
 
             if size == 0:
                 assert len(chunks) == 1, 'last zero size'
@@ -310,7 +310,7 @@ class TestHTTP:
 
     def form_url_encode(self, fields):
         data = "&".join(
-            "%s=%s" % (name, value) for name, value in fields.items()
+            f'{name}={value}' for name, value in fields.items()
         ).encode()
         return data, 'application/x-www-form-urlencoded'
 
@@ -341,21 +341,21 @@ class TestHTTP:
             else:
                 pytest.fail('multipart requires a string or stream data')
 
-            body += ("--%s\r\nContent-Disposition: form-data; name=\"%s\"") % (
-                boundary,
-                field,
+            body += (
+                f'--{boundary}\r\nContent-Disposition: form-data;'
+                f'name="{field}"'
             )
 
             if filename != '':
-                body += "; filename=\"%s\"" % filename
+                body += f'; filename="{filename}"'
 
-            body += "\r\n"
+            body += '\r\n'
 
             if datatype != '':
-                body += "Content-Type: %s\r\n" % datatype
+                body += f'Content-Type: {datatype}\r\n'
 
-            body += "\r\n%s\r\n" % data
+            body += f'\r\n{data}\r\n'
 
-        body += "--%s--\r\n" % boundary
+        body += f'--{boundary}--\r\n'
 
-        return body.encode(), "multipart/form-data; boundary=%s" % boundary
+        return body.encode(), f'multipart/form-data; boundary={boundary}'
diff --git a/test/unit/log.py b/test/unit/log.py
index 7263443d..f984d7a1 100644
--- a/test/unit/log.py
+++ b/test/unit/log.py
@@ -20,4 +20,4 @@ class Log:
         Log.pos[name] = pos
 
     def get_path(name=UNIT_LOG):
-        return Log.temp_dir + '/' + name
+        return f'{Log.temp_dir}/{name}'
diff --git a/test/unit/utils.py b/test/unit/utils.py
index d6590b97..985801e2 100644
--- a/test/unit/utils.py
+++ b/test/unit/utils.py
@@ -69,7 +69,7 @@ def waitforsocket(port):
             except KeyboardInterrupt:
                 raise
 
-    pytest.fail('Can\'t connect to the 127.0.0.1:' + str(port))
+    pytest.fail(f"Can't connect to the 127.0.0.1:{port}")
 
 
 def check_findmnt():
@@ -125,7 +125,7 @@ def getns(nstype):
     # read namespace id from symlink file:
     # it points to: '<nstype>:[<ns id>]'
     # # eg.: 'pid:[4026531836]'
-    nspath = '/proc/self/ns/' + nstype
+    nspath = f'/proc/self/ns/{nstype}'
     data = None
 
     if os.path.exists(nspath):