add new_child method to span class

aiozipkin/span.py

@@ -66,6 +66,10 @@ def kind(self: T, span_kind: str) -> T:
     def name(self: T, span_name: str) -> T:
         pass  # pragma: no cover
 
+    @abstractmethod
+    def new_child(self: T, name: str = None, kind: str = None) -> T:
+        pass  # pragma: no cover
+
     def __enter__(self: T) -> T:
         self.start()
         return self
@@ -117,6 +121,9 @@ def kind(self, span_kind: str) -> 'NoopSpan':
     def name(self, span_name: str) -> 'NoopSpan':
         return self
 
+    def new_child(self, name: str = None, kind: str = None) -> 'NoopSpan':
+        return self
+
 
 class Span(SpanAbc):
     def __init__(self, tracer: 'Tracer',
@@ -177,3 +184,11 @@ def kind(self, span_kind: str) -> 'Span':
     def name(self, span_name: str) -> 'Span':
         self._record.name(span_name)
         return self
+
+    def new_child(self, name: str = None, kind: str = None) -> 'Span':
+        span = self.tracer.new_child(self.context)
+        if name is not None:
+            span.name(name)
+        if kind is not None:
+            span.kind(kind)
+        return span  # type: ignore