How to use the gunicorn.util.http_date function in gunicorn

def test_http_date():
    assert util.http_date(1508607753.740316) == 'Sat, 21 Oct 2017 17:42:33 GMT'

def default_headers(self):
        # set the connection header
        if self.upgrade:
            connection = "upgrade"
        elif self.should_close():
            connection = "close"
        else:
            connection = "keep-alive"

        headers = [
            "HTTP/%s.%s %s\r\n" % (self.req.version[0],
                self.req.version[1], self.status),
            "Server: %s\r\n" % self.version,
            "Date: %s\r\n" % util.http_date(),
            "Connection: %s\r\n" % connection
        ]
        if self.chunked:
            headers.append("Transfer-Encoding: chunked\r\n")
        return headers

def default_headers(self):
        # set the connection header
        if self.upgrade:
            connection = "upgrade"
        elif self.should_close():
            connection = "close"
        else:
            connection = "keep-alive"

        headers = [
            "HTTP/%s.%s %s\r\n" % (self.req.version[0],
                self.req.version[1], self.status),
            "Server: %s\r\n" % self.version,
            "Date: %s\r\n" % util.http_date(),
            "Connection: %s\r\n" % connection
        ]
        if self.chunked:
            headers.append("Transfer-Encoding: chunked\r\n")
        return headers

def default_headers(self):
        # set the connection header
        if self.upgrade:
            connection = "upgrade"
        elif self.should_close():
            connection = "close"
        else:
            connection = "keep-alive"

        headers = [
            "HTTP/%s.%s %s\r\n" % (self.req.version[0],
                self.req.version[1], self.status),
            "Server: %s\r\n" % self.version,
            "Date: %s\r\n" % util.http_date(),
            "Connection: %s\r\n" % connection
        ]
        if self.chunked:
            headers.append("Transfer-Encoding: chunked\r\n")
        return headers

def default_headers(self):
        # set the connection header
        if self.upgrade:
            connection = "upgrade"
        elif self.should_close():
            connection = "close"
        else:
            connection = "keep-alive"

        headers = [
            "HTTP/%s.%s %s\r\n" % (self.req.version[0],
                self.req.version[1], self.status),
            "Server: %s\r\n" % self.version,
            "Date: %s\r\n" % util.http_date(),
            "Connection: %s\r\n" % connection
        ]
        if self.chunked:
            headers.append("Transfer-Encoding: chunked\r\n")
        return headers

def default_headers(self):
        return [
            "HTTP/1.1 %s\r\n" % self.status,
            "Server: %s\r\n" % self.version,
            "Date: %s\r\n" % http_date(),
            "Connection: close\r\n"
        ]