Validate type with writing to captured output like without

Fixes https://github.com/pytest-dev/pytest/issues/4861.

changelog/4861.bugfix.rst

@@ -0,0 +1 @@
+Validate type with writing to captured output like without.

src/_pytest/capture.py

@@ -17,6 +17,7 @@ from tempfile import TemporaryFile
 import six
 
 import pytest
+from _pytest.compat import _PY3
 from _pytest.compat import CaptureIO
 
 patchsysdict = {0: "stdin", 1: "stdout", 2: "stderr"}
@@ -412,6 +413,10 @@ class EncodedFile(object):
     def write(self, obj):
         if isinstance(obj, six.text_type):
             obj = obj.encode(self.encoding, "replace")
+        elif _PY3:
+            raise TypeError(
+                "write() argument must be str, not {}".format(type(obj).__name__)
+            )
         self.buffer.write(obj)
 
     def writelines(self, linelist):

testing/test_capture.py

@@ -18,6 +18,7 @@ from six import text_type
 import pytest
 from _pytest import capture
 from _pytest.capture import CaptureManager
+from _pytest.compat import _PY3
 from _pytest.main import EXIT_NOTESTSCOLLECTED
 
 # note: py.io capture tests where copied from
@@ -1526,3 +1527,26 @@ def test_capture_with_live_logging(testdir, capture_fixture):
 
     result = testdir.runpytest_subprocess("--log-cli-level=INFO")
     assert result.ret == 0
+
+
+def test_typeerror_encodedfile_write(testdir):
+    """It should behave the same with and without output capturing (#4861)."""
+    p = testdir.makepyfile(
+        """
+        def test_fails():
+            import sys
+            sys.stdout.write(b"foo")
+    """
+    )
+    result_without_capture = testdir.runpytest("-s", str(p))
+
+    result_with_capture = testdir.runpytest(str(p))
+
+    assert result_with_capture.ret == result_without_capture.ret
+
+    if _PY3:
+        result_with_capture.stdout.fnmatch_lines(
+            ["E           TypeError: write() argument must be str, not bytes"]
+        )
+    else:
+        assert result_with_capture.ret == 0