Do not print (duplicate) INTERNALERROR with --pdb

changelog/4132.bugfix.rst

@@ -0,0 +1 @@
+Fix duplicate printing of internal errors when using ``--pdb``.

src/_pytest/debugging.py

@@ -109,9 +109,6 @@ def pytest_exception_interact(self, node, call, report):
         _enter_pdb(node, call.excinfo, report)
 
     def pytest_internalerror(self, excrepr, excinfo):
-        for line in str(excrepr).split("\n"):
-            sys.stderr.write("INTERNALERROR> %s\n" % line)
-            sys.stderr.flush()
         tb = _postmortem_traceback(excinfo)
         post_mortem(tb)
 

testing/test_pdb.py

@@ -334,8 +334,20 @@ def pytest_runtest_protocol():
         )
         p1 = testdir.makepyfile("def test_func(): pass")
         child = testdir.spawn_pytest("--pdb %s" % p1)
-        # child.expect(".*import pytest.*")
         child.expect("Pdb")
+
+        # INTERNALERROR is only displayed once via terminal reporter.
+        assert (
+            len(
+                [
+                    x
+                    for x in child.before.decode().splitlines()
+                    if x.startswith("INTERNALERROR> Traceback")
+                ]
+            )
+            == 1
+        )
+
         child.sendeof()
         self.flush(child)
 
@@ -345,7 +357,7 @@ def test_pdb_interaction_capturing_simple(self, testdir):
             import pytest
             def test_1():
                 i = 0
-                print ("hello17")
+                print("hello17")
                 pytest.set_trace()
                 x = 3
         """
@@ -383,7 +395,7 @@ def test_pdb_and_capsys(self, testdir):
             """
             import pytest
             def test_1(capsys):
-                print ("hello1")
+                print("hello1")
                 pytest.set_trace()
         """
         )
@@ -420,7 +432,7 @@ def test_set_trace_capturing_afterwards(self, testdir):
             def test_1():
                 pdb.set_trace()
             def test_2():
-                print ("hello")
+                print("hello")
                 assert 0
         """
         )
@@ -461,10 +473,10 @@ def test_pdb_interaction_capturing_twice(self, testdir):
             import pytest
             def test_1():
                 i = 0
-                print ("hello17")
+                print("hello17")
                 pytest.set_trace()
                 x = 3
-                print ("hello18")
+                print("hello18")
                 pytest.set_trace()
                 x = 4
         """
@@ -525,7 +537,7 @@ def test_enter_pdb_hook_is_called(self, testdir):
             """
             def pytest_enter_pdb(config):
                 assert config.testing_verification == 'configured'
-                print 'enter_pdb_hook'
+                print('enter_pdb_hook')
 
             def pytest_configure(config):
                 config.testing_verification = 'configured'
@@ -562,7 +574,7 @@ def test_pdb_custom_cls_with_settrace(self, testdir, monkeypatch):
             custom_pdb="""
             class CustomPdb(object):
                 def set_trace(*args, **kwargs):
-                    print 'custom set_trace>'
+                    print('custom set_trace>')
          """
         )
         p1 = testdir.makepyfile(