diff --git a/Lib/tabnanny.py b/Lib/tabnanny.py
new file mode 100755
index 000000000..7973f26f9
--- /dev/null
+++ b/Lib/tabnanny.py
@@ -0,0 +1,333 @@
+#! /usr/bin/env python3
+
+"""The Tab Nanny despises ambiguous indentation.  She knows no mercy.
+
+tabnanny -- Detection of ambiguous indentation
+
+For the time being this module is intended to be called as a script.
+However it is possible to import it into an IDE and use the function
+check() described below.
+
+Warning: The API provided by this module is likely to change in future
+releases; such changes may not be backward compatible.
+"""
+
+# Released to the public domain, by Tim Peters, 15 April 1998.
+
+# XXX Note: this is now a standard library module.
+# XXX The API needs to undergo changes however; the current code is too
+# XXX script-like.  This will be addressed later.
+
+__version__ = "6"
+
+import os
+import sys
+import tokenize
+if not hasattr(tokenize, 'NL'):
+    raise ValueError("tokenize.NL doesn't exist -- tokenize module too old")
+
+__all__ = ["check", "NannyNag", "process_tokens"]
+
+verbose = 0
+filename_only = 0
+
+def errprint(*args):
+    sep = ""
+    for arg in args:
+        sys.stderr.write(sep + str(arg))
+        sep = " "
+    sys.stderr.write("\n")
+
+def main():
+    import getopt
+
+    global verbose, filename_only
+    try:
+        opts, args = getopt.getopt(sys.argv[1:], "qv")
+    except getopt.error as msg:
+        errprint(msg)
+        return
+    for o, a in opts:
+        if o == '-q':
+            filename_only = filename_only + 1
+        if o == '-v':
+            verbose = verbose + 1
+    if not args:
+        errprint("Usage:", sys.argv[0], "[-v] file_or_directory ...")
+        return
+    for arg in args:
+        check(arg)
+
+class NannyNag(Exception):
+    """
+    Raised by process_tokens() if detecting an ambiguous indent.
+    Captured and handled in check().
+    """
+    def __init__(self, lineno, msg, line):
+        self.lineno, self.msg, self.line = lineno, msg, line
+    def get_lineno(self):
+        return self.lineno
+    def get_msg(self):
+        return self.msg
+    def get_line(self):
+        return self.line
+
+def check(file):
+    """check(file_or_dir)
+
+    If file_or_dir is a directory and not a symbolic link, then recursively
+    descend the directory tree named by file_or_dir, checking all .py files
+    along the way. If file_or_dir is an ordinary Python source file, it is
+    checked for whitespace related problems. The diagnostic messages are
+    written to standard output using the print statement.
+    """
+
+    if os.path.isdir(file) and not os.path.islink(file):
+        if verbose:
+            print("%r: listing directory" % (file,))
+        names = os.listdir(file)
+        for name in names:
+            fullname = os.path.join(file, name)
+            if (os.path.isdir(fullname) and
+                not os.path.islink(fullname) or
+                os.path.normcase(name[-3:]) == ".py"):
+                check(fullname)
+        return
+
+    try:
+        f = tokenize.open(file)
+    except OSError as msg:
+        errprint("%r: I/O Error: %s" % (file, msg))
+        return
+
+    if verbose > 1:
+        print("checking %r ..." % file)
+
+    try:
+        process_tokens(tokenize.generate_tokens(f.readline))
+
+    except tokenize.TokenError as msg:
+        errprint("%r: Token Error: %s" % (file, msg))
+        return
+
+    except IndentationError as msg:
+        errprint("%r: Indentation Error: %s" % (file, msg))
+        return
+
+    except NannyNag as nag:
+        badline = nag.get_lineno()
+        line = nag.get_line()
+        if verbose:
+            print("%r: *** Line %d: trouble in tab city! ***" % (file, badline))
+            print("offending line: %r" % (line,))
+            print(nag.get_msg())
+        else:
+            if ' ' in file: file = '"' + file + '"'
+            if filename_only: print(file)
+            else: print(file, badline, repr(line))
+        return
+
+    finally:
+        f.close()
+
+    if verbose:
+        print("%r: Clean bill of health." % (file,))
+
+class Whitespace:
+    # the characters used for space and tab
+    S, T = ' \t'
+
+    # members:
+    #   raw
+    #       the original string
+    #   n
+    #       the number of leading whitespace characters in raw
+    #   nt
+    #       the number of tabs in raw[:n]
+    #   norm
+    #       the normal form as a pair (count, trailing), where:
+    #       count
+    #           a tuple such that raw[:n] contains count[i]
+    #           instances of S * i + T
+    #       trailing
+    #           the number of trailing spaces in raw[:n]
+    #       It's A Theorem that m.indent_level(t) ==
+    #       n.indent_level(t) for all t >= 1 iff m.norm == n.norm.
+    #   is_simple
+    #       true iff raw[:n] is of the form (T*)(S*)
+
+    def __init__(self, ws):
+        self.raw  = ws
+        S, T = Whitespace.S, Whitespace.T
+        count = []
+        b = n = nt = 0
+        for ch in self.raw:
+            if ch == S:
+                n = n + 1
+                b = b + 1
+            elif ch == T:
+                n = n + 1
+                nt = nt + 1
+                if b >= len(count):
+                    count = count + [0] * (b - len(count) + 1)
+                count[b] = count[b] + 1
+                b = 0
+            else:
+                break
+        self.n    = n
+        self.nt   = nt
+        self.norm = tuple(count), b
+        self.is_simple = len(count) <= 1
+
+    # return length of longest contiguous run of spaces (whether or not
+    # preceding a tab)
+    def longest_run_of_spaces(self):
+        count, trailing = self.norm
+        return max(len(count)-1, trailing)
+
+    def indent_level(self, tabsize):
+        # count, il = self.norm
+        # for i in range(len(count)):
+        #    if count[i]:
+        #        il = il + (i//tabsize + 1)*tabsize * count[i]
+        # return il
+
+        # quicker:
+        # il = trailing + sum (i//ts + 1)*ts*count[i] =
+        # trailing + ts * sum (i//ts + 1)*count[i] =
+        # trailing + ts * sum i//ts*count[i] + count[i] =
+        # trailing + ts * [(sum i//ts*count[i]) + (sum count[i])] =
+        # trailing + ts * [(sum i//ts*count[i]) + num_tabs]
+        # and note that i//ts*count[i] is 0 when i < ts
+
+        count, trailing = self.norm
+        il = 0
+        for i in range(tabsize, len(count)):
+            il = il + i//tabsize * count[i]
+        return trailing + tabsize * (il + self.nt)
+
+    # return true iff self.indent_level(t) == other.indent_level(t)
+    # for all t >= 1
+    def equal(self, other):
+        return self.norm == other.norm
+
+    # return a list of tuples (ts, i1, i2) such that
+    # i1 == self.indent_level(ts) != other.indent_level(ts) == i2.
+    # Intended to be used after not self.equal(other) is known, in which
+    # case it will return at least one witnessing tab size.
+    def not_equal_witness(self, other):
+        n = max(self.longest_run_of_spaces(),
+                other.longest_run_of_spaces()) + 1
+        a = []
+        for ts in range(1, n+1):
+            if self.indent_level(ts) != other.indent_level(ts):
+                a.append( (ts,
+                           self.indent_level(ts),
+                           other.indent_level(ts)) )
+        return a
+
+    # Return True iff self.indent_level(t) < other.indent_level(t)
+    # for all t >= 1.
+    # The algorithm is due to Vincent Broman.
+    # Easy to prove it's correct.
+    # XXXpost that.
+    # Trivial to prove n is sharp (consider T vs ST).
+    # Unknown whether there's a faster general way.  I suspected so at
+    # first, but no longer.
+    # For the special (but common!) case where M and N are both of the
+    # form (T*)(S*), M.less(N) iff M.len() < N.len() and
+    # M.num_tabs() <= N.num_tabs(). Proof is easy but kinda long-winded.
+    # XXXwrite that up.
+    # Note that M is of the form (T*)(S*) iff len(M.norm[0]) <= 1.
+    def less(self, other):
+        if self.n >= other.n:
+            return False
+        if self.is_simple and other.is_simple:
+            return self.nt <= other.nt
+        n = max(self.longest_run_of_spaces(),
+                other.longest_run_of_spaces()) + 1
+        # the self.n >= other.n test already did it for ts=1
+        for ts in range(2, n+1):
+            if self.indent_level(ts) >= other.indent_level(ts):
+                return False
+        return True
+
+    # return a list of tuples (ts, i1, i2) such that
+    # i1 == self.indent_level(ts) >= other.indent_level(ts) == i2.
+    # Intended to be used after not self.less(other) is known, in which
+    # case it will return at least one witnessing tab size.
+    def not_less_witness(self, other):
+        n = max(self.longest_run_of_spaces(),
+                other.longest_run_of_spaces()) + 1
+        a = []
+        for ts in range(1, n+1):
+            if self.indent_level(ts) >= other.indent_level(ts):
+                a.append( (ts,
+                           self.indent_level(ts),
+                           other.indent_level(ts)) )
+        return a
+
+def format_witnesses(w):
+    firsts = (str(tup[0]) for tup in w)
+    prefix = "at tab size"
+    if len(w) > 1:
+        prefix = prefix + "s"
+    return prefix + " " + ', '.join(firsts)
+
+def process_tokens(tokens):
+    INDENT = tokenize.INDENT
+    DEDENT = tokenize.DEDENT
+    NEWLINE = tokenize.NEWLINE
+    JUNK = tokenize.COMMENT, tokenize.NL
+    indents = [Whitespace("")]
+    check_equal = 0
+
+    for (type, token, start, end, line) in tokens:
+        if type == NEWLINE:
+            # a program statement, or ENDMARKER, will eventually follow,
+            # after some (possibly empty) run of tokens of the form
+            #     (NL | COMMENT)* (INDENT | DEDENT+)?
+            # If an INDENT appears, setting check_equal is wrong, and will
+            # be undone when we see the INDENT.
+            check_equal = 1
+
+        elif type == INDENT:
+            check_equal = 0
+            thisguy = Whitespace(token)
+            if not indents[-1].less(thisguy):
+                witness = indents[-1].not_less_witness(thisguy)
+                msg = "indent not greater e.g. " + format_witnesses(witness)
+                raise NannyNag(start[0], msg, line)
+            indents.append(thisguy)
+
+        elif type == DEDENT:
+            # there's nothing we need to check here!  what's important is
+            # that when the run of DEDENTs ends, the indentation of the
+            # program statement (or ENDMARKER) that triggered the run is
+            # equal to what's left at the top of the indents stack
+
+            # Ouch!  This assert triggers if the last line of the source
+            # is indented *and* lacks a newline -- then DEDENTs pop out
+            # of thin air.
+            # assert check_equal  # else no earlier NEWLINE, or an earlier INDENT
+            check_equal = 1
+
+            del indents[-1]
+
+        elif check_equal and type not in JUNK:
+            # this is the first "real token" following a NEWLINE, so it
+            # must be the first token of the next program statement, or an
+            # ENDMARKER; the "line" argument exposes the leading whitespace
+            # for this statement; in the case of ENDMARKER, line is an empty
+            # string, so will properly match the empty string with which the
+            # "indents" stack was seeded
+            check_equal = 0
+            thisguy = Whitespace(line)
+            if not indents[-1].equal(thisguy):
+                witness = indents[-1].not_equal_witness(thisguy)
+                msg = "indent not equal e.g. " + format_witnesses(witness)
+                raise NannyNag(start[0], msg, line)
+
+
+if __name__ == '__main__':
+    main()
diff --git a/Lib/test/test_tabnanny.py b/Lib/test/test_tabnanny.py
new file mode 100644
index 000000000..e0a82e95c
--- /dev/null
+++ b/Lib/test/test_tabnanny.py
@@ -0,0 +1,346 @@
+"""Testing `tabnanny` module.
+
+Glossary:
+    * errored    : Whitespace related problems present in file.
+"""
+from unittest import TestCase, mock
+import errno
+import os
+import tabnanny
+import tokenize
+import tempfile
+import textwrap
+from test.support import (captured_stderr, captured_stdout, script_helper,
+                          findfile)
+from test.support.os_helper import unlink
+
+
+SOURCE_CODES = {
+    "incomplete_expression": (
+        'fruits = [\n'
+        '    "Apple",\n'
+        '    "Orange",\n'
+        '    "Banana",\n'
+        '\n'
+        'print(fruits)\n'
+    ),
+    "wrong_indented": (
+        'if True:\n'
+        '    print("hello")\n'
+        '  print("world")\n'
+        'else:\n'
+        '    print("else called")\n'
+    ),
+    "nannynag_errored": (
+        'if True:\n'
+        ' \tprint("hello")\n'
+        '\tprint("world")\n'
+        'else:\n'
+        '    print("else called")\n'
+    ),
+    "error_free": (
+        'if True:\n'
+        '    print("hello")\n'
+        '    print("world")\n'
+        'else:\n'
+        '    print("else called")\n'
+    ),
+    "tab_space_errored_1": (
+        'def my_func():\n'
+        '\t  print("hello world")\n'
+        '\t  if True:\n'
+        '\t\tprint("If called")'
+    ),
+    "tab_space_errored_2": (
+        'def my_func():\n'
+        '\t\tprint("Hello world")\n'
+        '\t\tif True:\n'
+        '\t        print("If called")'
+    )
+}
+
+
+class TemporaryPyFile:
+    """Create a temporary python source code file."""
+
+    def __init__(self, source_code='', directory=None):
+        self.source_code = source_code
+        self.dir = directory
+
+    def __enter__(self):
+        with tempfile.NamedTemporaryFile(
+            mode='w', dir=self.dir, suffix=".py", delete=False
+        ) as f:
+            f.write(self.source_code)
+        self.file_path = f.name
+        return self.file_path
+
+    def __exit__(self, exc_type, exc_value, exc_traceback):
+        unlink(self.file_path)
+
+
+class TestFormatWitnesses(TestCase):
+    """Testing `tabnanny.format_witnesses()`."""
+
+    def test_format_witnesses(self):
+        """Asserting formatter result by giving various input samples."""
+        tests = [
+            ('Test', 'at tab sizes T, e, s, t'),
+            ('', 'at tab size '),
+            ('t', 'at tab size t'),
+            ('  t  ', 'at tab sizes  ,  , t,  ,  '),
+        ]
+
+        for words, expected in tests:
+            with self.subTest(words=words, expected=expected):
+                self.assertEqual(tabnanny.format_witnesses(words), expected)
+
+
+class TestErrPrint(TestCase):
+    """Testing `tabnanny.errprint()`."""
+
+    def test_errprint(self):
+        """Asserting result of `tabnanny.errprint()` by giving sample inputs."""
+        tests = [
+            (['first', 'second'], 'first second\n'),
+            (['first'], 'first\n'),
+            ([1, 2, 3], '1 2 3\n'),
+            ([], '\n')
+        ]
+
+        for args, expected in tests:
+            with self.subTest(arguments=args, expected=expected):
+                with captured_stderr() as stderr:
+                    tabnanny.errprint(*args)
+                self.assertEqual(stderr.getvalue() , expected)
+
+
+class TestNannyNag(TestCase):
+    def test_all_methods(self):
+        """Asserting behaviour of `tabnanny.NannyNag` exception."""
+        tests = [
+            (
+                tabnanny.NannyNag(0, "foo", "bar"),
+                {'lineno': 0, 'msg': 'foo', 'line': 'bar'}
+            ),
+            (
+                tabnanny.NannyNag(5, "testmsg", "testline"),
+                {'lineno': 5, 'msg': 'testmsg', 'line': 'testline'}
+            )
+        ]
+        for nanny, expected in tests:
+            line_number = nanny.get_lineno()
+            msg = nanny.get_msg()
+            line = nanny.get_line()
+            with self.subTest(
+                line_number=line_number, expected=expected['lineno']
+            ):
+                self.assertEqual(expected['lineno'], line_number)
+            with self.subTest(msg=msg, expected=expected['msg']):
+                self.assertEqual(expected['msg'], msg)
+            with self.subTest(line=line, expected=expected['line']):
+                self.assertEqual(expected['line'], line)
+
+
+class TestCheck(TestCase):
+    """Testing tabnanny.check()."""
+
+    def setUp(self):
+        self.addCleanup(setattr, tabnanny, 'verbose', tabnanny.verbose)
+        tabnanny.verbose = 0  # Forcefully deactivating verbose mode.
+
+    def verify_tabnanny_check(self, dir_or_file, out="", err=""):
+        """Common verification for tabnanny.check().
+
+        Use this method to assert expected values of `stdout` and `stderr` after
+        running tabnanny.check() on given `dir` or `file` path. Because
+        tabnanny.check() captures exceptions and writes to `stdout` and
+        `stderr`, asserting standard outputs is the only way.
+        """
+        with captured_stdout() as stdout, captured_stderr() as stderr:
+            tabnanny.check(dir_or_file)
+        self.assertEqual(stdout.getvalue(), out)
+        self.assertEqual(stderr.getvalue(), err)
+
+    def test_correct_file(self):
+        """A python source code file without any errors."""
+        with TemporaryPyFile(SOURCE_CODES["error_free"]) as file_path:
+            self.verify_tabnanny_check(file_path)
+
+    def test_correct_directory_verbose(self):
+        """Directory containing few error free python source code files.
+
+        Because order of files returned by `os.lsdir()` is not fixed, verify the
+        existence of each output lines at `stdout` using `in` operator.
+        `verbose` mode of `tabnanny.verbose` asserts `stdout`.
+        """
+        with tempfile.TemporaryDirectory() as tmp_dir:
+            lines = [f"{tmp_dir!r}: listing directory\n",]
+            file1 = TemporaryPyFile(SOURCE_CODES["error_free"], directory=tmp_dir)
+            file2 = TemporaryPyFile(SOURCE_CODES["error_free"], directory=tmp_dir)
+            with file1 as file1_path, file2 as file2_path:
+                for file_path in (file1_path, file2_path):
+                    lines.append(f"{file_path!r}: Clean bill of health.\n")
+
+                tabnanny.verbose = 1
+                with captured_stdout() as stdout, captured_stderr() as stderr:
+                    tabnanny.check(tmp_dir)
+                stdout = stdout.getvalue()
+                for line in lines:
+                    with self.subTest(line=line):
+                        self.assertIn(line, stdout)
+                self.assertEqual(stderr.getvalue(), "")
+
+    def test_correct_directory(self):
+        """Directory which contains few error free python source code files."""
+        with tempfile.TemporaryDirectory() as tmp_dir:
+            with TemporaryPyFile(SOURCE_CODES["error_free"], directory=tmp_dir):
+                self.verify_tabnanny_check(tmp_dir)
+
+    def test_when_wrong_indented(self):
+        """A python source code file eligible for raising `IndentationError`."""
+        with TemporaryPyFile(SOURCE_CODES["wrong_indented"]) as file_path:
+            err = ('unindent does not match any outer indentation level'
+                ' (<tokenize>, line 3)\n')
+            err = f"{file_path!r}: Indentation Error: {err}"
+            self.verify_tabnanny_check(file_path, err=err)
+
+    def test_when_tokenize_tokenerror(self):
+        """A python source code file eligible for raising 'tokenize.TokenError'."""
+        with TemporaryPyFile(SOURCE_CODES["incomplete_expression"]) as file_path:
+            err = "('EOF in multi-line statement', (7, 0))\n"
+            err = f"{file_path!r}: Token Error: {err}"
+            self.verify_tabnanny_check(file_path, err=err)
+
+    def test_when_nannynag_error_verbose(self):
+        """A python source code file eligible for raising `tabnanny.NannyNag`.
+
+        Tests will assert `stdout` after activating `tabnanny.verbose` mode.
+        """
+        with TemporaryPyFile(SOURCE_CODES["nannynag_errored"]) as file_path:
+            out = f"{file_path!r}: *** Line 3: trouble in tab city! ***\n"
+            out += "offending line: '\\tprint(\"world\")\\n'\n"
+            out += "indent not equal e.g. at tab size 1\n"
+
+            tabnanny.verbose = 1
+            self.verify_tabnanny_check(file_path, out=out)
+
+    def test_when_nannynag_error(self):
+        """A python source code file eligible for raising `tabnanny.NannyNag`."""
+        with TemporaryPyFile(SOURCE_CODES["nannynag_errored"]) as file_path:
+            out = f"{file_path} 3 '\\tprint(\"world\")\\n'\n"
+            self.verify_tabnanny_check(file_path, out=out)
+
+    def test_when_no_file(self):
+        """A python file which does not exist actually in system."""
+        path = 'no_file.py'
+        err = (f"{path!r}: I/O Error: [Errno {errno.ENOENT}] "
+              f"{os.strerror(errno.ENOENT)}: {path!r}\n")
+        self.verify_tabnanny_check(path, err=err)
+
+    def test_errored_directory(self):
+        """Directory containing wrongly indented python source code files."""
+        with tempfile.TemporaryDirectory() as tmp_dir:
+            error_file = TemporaryPyFile(
+                SOURCE_CODES["wrong_indented"], directory=tmp_dir
+            )
+            code_file = TemporaryPyFile(
+                SOURCE_CODES["error_free"], directory=tmp_dir
+            )
+            with error_file as e_file, code_file as c_file:
+                err = ('unindent does not match any outer indentation level'
+                            ' (<tokenize>, line 3)\n')
+                err = f"{e_file!r}: Indentation Error: {err}"
+                self.verify_tabnanny_check(tmp_dir, err=err)
+
+
+class TestProcessTokens(TestCase):
+    """Testing `tabnanny.process_tokens()`."""
+
+    @mock.patch('tabnanny.NannyNag')
+    def test_with_correct_code(self, MockNannyNag):
+        """A python source code without any whitespace related problems."""
+
+        with TemporaryPyFile(SOURCE_CODES["error_free"]) as file_path:
+            with open(file_path) as f:
+                tabnanny.process_tokens(tokenize.generate_tokens(f.readline))
+            self.assertFalse(MockNannyNag.called)
+
+    def test_with_errored_codes_samples(self):
+        """A python source code with whitespace related sampled problems."""
+
+        # "tab_space_errored_1": executes block under type == tokenize.INDENT
+        #                        at `tabnanny.process_tokens()`.
+        # "tab space_errored_2": executes block under
+        #                        `check_equal and type not in JUNK` condition at
+        #                        `tabnanny.process_tokens()`.
+
+        for key in ["tab_space_errored_1", "tab_space_errored_2"]:
+            with self.subTest(key=key):
+                with TemporaryPyFile(SOURCE_CODES[key]) as file_path:
+                    with open(file_path) as f:
+                        tokens = tokenize.generate_tokens(f.readline)
+                        with self.assertRaises(tabnanny.NannyNag):
+                            tabnanny.process_tokens(tokens)
+
+
+class TestCommandLine(TestCase):
+    """Tests command line interface of `tabnanny`."""
+
+    def validate_cmd(self, *args, stdout="", stderr="", partial=False):
+        """Common function to assert the behaviour of command line interface."""
+        _, out, err = script_helper.assert_python_ok('-m', 'tabnanny', *args)
+        # Note: The `splitlines()` will solve the problem of CRLF(\r) added
+        # by OS Windows.
+        out = os.fsdecode(out)
+        err = os.fsdecode(err)
+        if partial:
+            for std, output in ((stdout, out), (stderr, err)):
+                _output = output.splitlines()
+                for _std in std.splitlines():
+                    with self.subTest(std=_std, output=_output):
+                        self.assertIn(_std, _output)
+        else:
+            self.assertListEqual(out.splitlines(), stdout.splitlines())
+            self.assertListEqual(err.splitlines(), stderr.splitlines())
+
+    def test_with_errored_file(self):
+        """Should displays error when errored python file is given."""
+        with TemporaryPyFile(SOURCE_CODES["wrong_indented"]) as file_path:
+            stderr  = f"{file_path!r}: Indentation Error: "
+            stderr += ('unindent does not match any outer indentation level'
+                    ' (<tokenize>, line 3)')
+            self.validate_cmd(file_path, stderr=stderr)
+
+    def test_with_error_free_file(self):
+        """Should not display anything if python file is correctly indented."""
+        with TemporaryPyFile(SOURCE_CODES["error_free"]) as file_path:
+            self.validate_cmd(file_path)
+
+    def test_command_usage(self):
+        """Should display usage on no arguments."""
+        path = findfile('tabnanny.py')
+        stderr = f"Usage: {path} [-v] file_or_directory ..."
+        self.validate_cmd(stderr=stderr)
+
+    def test_quiet_flag(self):
+        """Should display less when quite mode is on."""
+        with TemporaryPyFile(SOURCE_CODES["nannynag_errored"]) as file_path:
+            stdout = f"{file_path}\n"
+            self.validate_cmd("-q", file_path, stdout=stdout)
+
+    def test_verbose_mode(self):
+        """Should display more error information if verbose mode is on."""
+        with TemporaryPyFile(SOURCE_CODES["nannynag_errored"]) as path:
+            stdout = textwrap.dedent(
+                "offending line: '\\tprint(\"world\")\\n'"
+            ).strip()
+            self.validate_cmd("-v", path, stdout=stdout, partial=True)
+
+    def test_double_verbose_mode(self):
+        """Should display detailed error information if double verbose is on."""
+        with TemporaryPyFile(SOURCE_CODES["nannynag_errored"]) as path:
+            stdout = textwrap.dedent(
+                "offending line: '\\tprint(\"world\")\\n'"
+            ).strip()
+            self.validate_cmd("-vv", path, stdout=stdout, partial=True)