improve PYTEST_DEBUG tracing output

by putingextra data on a new lines
with additional indent

_pytest/core.py

@@ -24,12 +24,28 @@ class TagTracer:
     def get(self, name):
         return TagTracerSub(self, (name,))
 
+    def format_message(self, tags, args):
+        if isinstance(args[-1], dict):
+            extra = args[-1]
+            args = args[:-1]
+        else:
+            extra = {}
+
+        content = " ".join(map(str, args))
+        indent = "  " * self.indent
+        
+        lines = [
+            "%s%s [%s]\n" %(indent, content, ":".join(tags))
+        ]
+
+        for name, value in extra.items():
+            lines.append("%s    %s: %s\n" % (indent, name, value))
+        return lines
+
     def processmessage(self, tags, args):
-        if self.writer is not None:
-            if args:
-                indent = "  " * self.indent
-                content = " ".join(map(str, args))
-                self.writer("%s%s [%s]\n" %(indent, content, ":".join(tags)))
+        if self.writer is not None and args:
+            lines = self.format_message(tags, args)
+            self.writer(''.join(lines))
         try:
             self._tag2proc[tags](tags, args)
         except KeyError: