Tests: "if" option in access logging.

Conditional access logging was introduced here:
4c91bebb50

test/test_access_log.py

@@ -28,6 +28,10 @@ def set_format(log_format):
     ), 'access_log format'
 
 
+def set_if(condition):
+    assert 'success' in client.conf(f'"{condition}"', 'access_log/if')
+
+
 def test_access_log_keepalive(wait_for_record):
     load('mirror')
 
@@ -308,6 +312,62 @@ def test_access_log_variables(wait_for_record):
     ), '$body_bytes_sent'
 
 
+def test_access_log_if(search_in_file, wait_for_record):
+    load('empty')
+    set_format('$uri')
+
+    def try_if(condition):
+        set_if(condition)
+        assert client.get(url=f'/{condition}')['status'] == 200
+
+    # const
+
+    try_if('')
+    try_if('0')
+    try_if('false')
+    try_if('undefined')
+    try_if('!')
+    try_if('!null')
+    try_if('1')
+
+    # variable
+
+    set_if('$arg_foo')
+    assert client.get(url='/bar?bar')['status'] == 200
+    assert client.get(url='/foo_empty?foo')['status'] == 200
+    assert client.get(url='/foo?foo=1')['status'] == 200
+
+    # check results
+
+    assert wait_for_record(r'^/foo$', 'access.log') is not None
+
+    assert search_in_file(r'^/$', 'access.log') is None
+    assert search_in_file(r'^/0$', 'access.log') is None
+    assert search_in_file(r'^/false$', 'access.log') is None
+    assert search_in_file(r'^/undefined$', 'access.log') is None
+    assert search_in_file(r'^/!$', 'access.log') is not None
+    assert search_in_file(r'^/!null$', 'access.log') is not None
+    assert search_in_file(r'^/1$', 'access.log') is not None
+
+    assert search_in_file(r'^/bar$', 'access.log') is None
+    assert search_in_file(r'^/foo_empty$', 'access.log') is None
+
+
+def test_access_log_if_njs(require, search_in_file, wait_for_record):
+    require({'modules': {'njs': 'any'}})
+
+    load('empty')
+    set_format('$uri')
+
+    set_if('`${args.foo == \'1\'}`')
+
+    assert client.get(url='/foo_2?foo=2')['status'] == 200
+    assert client.get(url='/foo_1?foo=1')['status'] == 200
+
+    assert wait_for_record(r'^/foo_1$', 'access.log') is not None
+    assert search_in_file(r'^/foo_2$', 'access.log') is None
+
+
 def test_access_log_incorrect(temp_dir, skip_alert):
     skip_alert(r'failed to apply new conf')
 
@@ -323,3 +383,5 @@ def test_access_log_incorrect(temp_dir, skip_alert):
         },
         'access_log',
     ), 'access_log format incorrect'
+
+    assert 'error' in client.conf('$arg_', 'access_log/if')