diff --git a/Lib/modulefinder.py b/Lib/modulefinder.py
new file mode 100644
index 0000000000..cb455f40c4
--- /dev/null
+++ b/Lib/modulefinder.py
@@ -0,0 +1,685 @@
+"""Find modules used by a script, using introspection."""
+
+import dis
+import importlib._bootstrap_external
+import importlib.machinery
+import marshal
+import os
+import io
+import sys
+
+
+LOAD_CONST = dis.opmap['LOAD_CONST']
+IMPORT_NAME = dis.opmap['IMPORT_NAME']
+STORE_NAME = dis.opmap['STORE_NAME']
+STORE_GLOBAL = dis.opmap['STORE_GLOBAL']
+STORE_OPS = STORE_NAME, STORE_GLOBAL
+EXTENDED_ARG = dis.EXTENDED_ARG
+
+# Old imp constants:
+
+_SEARCH_ERROR = 0
+_PY_SOURCE = 1
+_PY_COMPILED = 2
+_C_EXTENSION = 3
+_PKG_DIRECTORY = 5
+_C_BUILTIN = 6
+_PY_FROZEN = 7
+
+# Modulefinder does a good job at simulating Python's, but it can not
+# handle __path__ modifications packages make at runtime.  Therefore there
+# is a mechanism whereby you can register extra paths in this map for a
+# package, and it will be honored.
+
+# Note this is a mapping is lists of paths.
+packagePathMap = {}
+
+# A Public interface
+def AddPackagePath(packagename, path):
+    packagePathMap.setdefault(packagename, []).append(path)
+
+replacePackageMap = {}
+
+# This ReplacePackage mechanism allows modulefinder to work around
+# situations in which a package injects itself under the name
+# of another package into sys.modules at runtime by calling
+# ReplacePackage("real_package_name", "faked_package_name")
+# before running ModuleFinder.
+
+def ReplacePackage(oldname, newname):
+    replacePackageMap[oldname] = newname
+
+
+def _find_module(name, path=None):
+    """An importlib reimplementation of imp.find_module (for our purposes)."""
+
+    # It's necessary to clear the caches for our Finder first, in case any
+    # modules are being added/deleted/modified at runtime. In particular,
+    # test_modulefinder.py changes file tree contents in a cache-breaking way:
+
+    importlib.machinery.PathFinder.invalidate_caches()
+
+    spec = importlib.machinery.PathFinder.find_spec(name, path)
+
+    if spec is None:
+        raise ImportError("No module named {name!r}".format(name=name), name=name)
+
+    # Some special cases:
+
+    if spec.loader is importlib.machinery.BuiltinImporter:
+        return None, None, ("", "", _C_BUILTIN)
+
+    if spec.loader is importlib.machinery.FrozenImporter:
+        return None, None, ("", "", _PY_FROZEN)
+
+    file_path = spec.origin
+
+    if spec.loader.is_package(name):
+        return None, os.path.dirname(file_path), ("", "", _PKG_DIRECTORY)
+
+    if isinstance(spec.loader, importlib.machinery.SourceFileLoader):
+        kind = _PY_SOURCE
+
+    elif isinstance(spec.loader, importlib.machinery.ExtensionFileLoader):
+        kind = _C_EXTENSION
+
+    elif isinstance(spec.loader, importlib.machinery.SourcelessFileLoader):
+        kind = _PY_COMPILED
+
+    else:  # Should never happen.
+        return None, None, ("", "", _SEARCH_ERROR)
+
+    file = io.open_code(file_path)
+    suffix = os.path.splitext(file_path)[-1]
+
+    return file, file_path, (suffix, "rb", kind)
+
+
+class Module:
+
+    def __init__(self, name, file=None, path=None):
+        self.__name__ = name
+        self.__file__ = file
+        self.__path__ = path
+        self.__code__ = None
+        # The set of global names that are assigned to in the module.
+        # This includes those names imported through starimports of
+        # Python modules.
+        self.globalnames = {}
+        # The set of starimports this module did that could not be
+        # resolved, ie. a starimport from a non-Python module.
+        self.starimports = {}
+
+    def __repr__(self):
+        s = "Module(%r" % (self.__name__,)
+        if self.__file__ is not None:
+            s = s + ", %r" % (self.__file__,)
+        if self.__path__ is not None:
+            s = s + ", %r" % (self.__path__,)
+        s = s + ")"
+        return s
+
+class ModuleFinder:
+
+    def __init__(self, path=None, debug=0, excludes=None, replace_paths=None):
+        if path is None:
+            path = sys.path
+        self.path = path
+        self.modules = {}
+        self.badmodules = {}
+        self.debug = debug
+        self.indent = 0
+        self.excludes = excludes if excludes is not None else []
+        self.replace_paths = replace_paths if replace_paths is not None else []
+        self.processed_paths = []   # Used in debugging only
+
+    def msg(self, level, str, *args):
+        if level <= self.debug:
+            for i in range(self.indent):
+                print("   ", end=' ')
+            print(str, end=' ')
+            for arg in args:
+                print(repr(arg), end=' ')
+            print()
+
+    def msgin(self, *args):
+        level = args[0]
+        if level <= self.debug:
+            self.indent = self.indent + 1
+            self.msg(*args)
+
+    def msgout(self, *args):
+        level = args[0]
+        if level <= self.debug:
+            self.indent = self.indent - 1
+            self.msg(*args)
+
+    def run_script(self, pathname):
+        self.msg(2, "run_script", pathname)
+        with io.open_code(pathname) as fp:
+            stuff = ("", "rb", _PY_SOURCE)
+            self.load_module('__main__', fp, pathname, stuff)
+
+    def load_file(self, pathname):
+        dir, name = os.path.split(pathname)
+        name, ext = os.path.splitext(name)
+        with io.open_code(pathname) as fp:
+            stuff = (ext, "rb", _PY_SOURCE)
+            self.load_module(name, fp, pathname, stuff)
+
+    def import_hook(self, name, caller=None, fromlist=None, level=-1):
+        self.msg(3, "import_hook", name, caller, fromlist, level)
+        parent = self.determine_parent(caller, level=level)
+        q, tail = self.find_head_package(parent, name)
+        m = self.load_tail(q, tail)
+        if not fromlist:
+            return q
+        if m.__path__:
+            self.ensure_fromlist(m, fromlist)
+        return None
+
+    def determine_parent(self, caller, level=-1):
+        self.msgin(4, "determine_parent", caller, level)
+        if not caller or level == 0:
+            self.msgout(4, "determine_parent -> None")
+            return None
+        pname = caller.__name__
+        if level >= 1: # relative import
+            if caller.__path__:
+                level -= 1
+            if level == 0:
+                parent = self.modules[pname]
+                assert parent is caller
+                self.msgout(4, "determine_parent ->", parent)
+                return parent
+            if pname.count(".") < level:
+                raise ImportError("relative importpath too deep")
+            pname = ".".join(pname.split(".")[:-level])
+            parent = self.modules[pname]
+            self.msgout(4, "determine_parent ->", parent)
+            return parent
+        if caller.__path__:
+            parent = self.modules[pname]
+            assert caller is parent
+            self.msgout(4, "determine_parent ->", parent)
+            return parent
+        if '.' in pname:
+            i = pname.rfind('.')
+            pname = pname[:i]
+            parent = self.modules[pname]
+            assert parent.__name__ == pname
+            self.msgout(4, "determine_parent ->", parent)
+            return parent
+        self.msgout(4, "determine_parent -> None")
+        return None
+
+    def find_head_package(self, parent, name):
+        self.msgin(4, "find_head_package", parent, name)
+        if '.' in name:
+            i = name.find('.')
+            head = name[:i]
+            tail = name[i+1:]
+        else:
+            head = name
+            tail = ""
+        if parent:
+            qname = "%s.%s" % (parent.__name__, head)
+        else:
+            qname = head
+        q = self.import_module(head, qname, parent)
+        if q:
+            self.msgout(4, "find_head_package ->", (q, tail))
+            return q, tail
+        if parent:
+            qname = head
+            parent = None
+            q = self.import_module(head, qname, parent)
+            if q:
+                self.msgout(4, "find_head_package ->", (q, tail))
+                return q, tail
+        self.msgout(4, "raise ImportError: No module named", qname)
+        raise ImportError("No module named " + qname)
+
+    def load_tail(self, q, tail):
+        self.msgin(4, "load_tail", q, tail)
+        m = q
+        while tail:
+            i = tail.find('.')
+            if i < 0: i = len(tail)
+            head, tail = tail[:i], tail[i+1:]
+            mname = "%s.%s" % (m.__name__, head)
+            m = self.import_module(head, mname, m)
+            if not m:
+                self.msgout(4, "raise ImportError: No module named", mname)
+                raise ImportError("No module named " + mname)
+        self.msgout(4, "load_tail ->", m)
+        return m
+
+    def ensure_fromlist(self, m, fromlist, recursive=0):
+        self.msg(4, "ensure_fromlist", m, fromlist, recursive)
+        for sub in fromlist:
+            if sub == "*":
+                if not recursive:
+                    all = self.find_all_submodules(m)
+                    if all:
+                        self.ensure_fromlist(m, all, 1)
+            elif not hasattr(m, sub):
+                subname = "%s.%s" % (m.__name__, sub)
+                submod = self.import_module(sub, subname, m)
+                if not submod:
+                    raise ImportError("No module named " + subname)
+
+    def find_all_submodules(self, m):
+        if not m.__path__:
+            return
+        modules = {}
+        # 'suffixes' used to be a list hardcoded to [".py", ".pyc"].
+        # But we must also collect Python extension modules - although
+        # we cannot separate normal dlls from Python extensions.
+        suffixes = []
+        suffixes += importlib.machinery.EXTENSION_SUFFIXES[:]
+        suffixes += importlib.machinery.SOURCE_SUFFIXES[:]
+        suffixes += importlib.machinery.BYTECODE_SUFFIXES[:]
+        for dir in m.__path__:
+            try:
+                names = os.listdir(dir)
+            except OSError:
+                self.msg(2, "can't list directory", dir)
+                continue
+            for name in names:
+                mod = None
+                for suff in suffixes:
+                    n = len(suff)
+                    if name[-n:] == suff:
+                        mod = name[:-n]
+                        break
+                if mod and mod != "__init__":
+                    modules[mod] = mod
+        return modules.keys()
+
+    def import_module(self, partname, fqname, parent):
+        self.msgin(3, "import_module", partname, fqname, parent)
+        try:
+            m = self.modules[fqname]
+        except KeyError:
+            pass
+        else:
+            self.msgout(3, "import_module ->", m)
+            return m
+        if fqname in self.badmodules:
+            self.msgout(3, "import_module -> None")
+            return None
+        if parent and parent.__path__ is None:
+            self.msgout(3, "import_module -> None")
+            return None
+        try:
+            fp, pathname, stuff = self.find_module(partname,
+                                                   parent and parent.__path__, parent)
+        except ImportError:
+            self.msgout(3, "import_module ->", None)
+            return None
+
+        try:
+            m = self.load_module(fqname, fp, pathname, stuff)
+        finally:
+            if fp:
+                fp.close()
+        if parent:
+            setattr(parent, partname, m)
+        self.msgout(3, "import_module ->", m)
+        return m
+
+    def load_module(self, fqname, fp, pathname, file_info):
+        suffix, mode, type = file_info
+        self.msgin(2, "load_module", fqname, fp and "fp", pathname)
+        if type == _PKG_DIRECTORY:
+            m = self.load_package(fqname, pathname)
+            self.msgout(2, "load_module ->", m)
+            return m
+        if type == _PY_SOURCE:
+            co = compile(fp.read(), pathname, 'exec')
+        elif type == _PY_COMPILED:
+            try:
+                data = fp.read()
+                importlib._bootstrap_external._classify_pyc(data, fqname, {})
+            except ImportError as exc:
+                self.msgout(2, "raise ImportError: " + str(exc), pathname)
+                raise
+            co = marshal.loads(memoryview(data)[16:])
+        else:
+            co = None
+        m = self.add_module(fqname)
+        m.__file__ = pathname
+        if co:
+            if self.replace_paths:
+                co = self.replace_paths_in_code(co)
+            m.__code__ = co
+            self.scan_code(co, m)
+        self.msgout(2, "load_module ->", m)
+        return m
+
+    def _add_badmodule(self, name, caller):
+        if name not in self.badmodules:
+            self.badmodules[name] = {}
+        if caller:
+            self.badmodules[name][caller.__name__] = 1
+        else:
+            self.badmodules[name]["-"] = 1
+
+    def _safe_import_hook(self, name, caller, fromlist, level=-1):
+        # wrapper for self.import_hook() that won't raise ImportError
+        if name in self.badmodules:
+            self._add_badmodule(name, caller)
+            return
+        try:
+            self.import_hook(name, caller, level=level)
+        except ImportError as msg:
+            self.msg(2, "ImportError:", str(msg))
+            self._add_badmodule(name, caller)
+        except SyntaxError as msg:
+            self.msg(2, "SyntaxError:", str(msg))
+            self._add_badmodule(name, caller)
+        else:
+            if fromlist:
+                for sub in fromlist:
+                    fullname = name + "." + sub
+                    if fullname in self.badmodules:
+                        self._add_badmodule(fullname, caller)
+                        continue
+                    try:
+                        self.import_hook(name, caller, [sub], level=level)
+                    except ImportError as msg:
+                        self.msg(2, "ImportError:", str(msg))
+                        self._add_badmodule(fullname, caller)
+
+    def scan_opcodes(self, co):
+        # Scan the code, and yield 'interesting' opcode combinations
+        code = co.co_code
+        names = co.co_names
+        consts = co.co_consts
+        opargs = [(op, arg) for _, op, arg in dis._unpack_opargs(code)
+                  if op != EXTENDED_ARG]
+        for i, (op, oparg) in enumerate(opargs):
+            if op in STORE_OPS:
+                yield "store", (names[oparg],)
+                continue
+            if (op == IMPORT_NAME and i >= 2
+                    and opargs[i-1][0] == opargs[i-2][0] == LOAD_CONST):
+                level = consts[opargs[i-2][1]]
+                fromlist = consts[opargs[i-1][1]]
+                if level == 0: # absolute import
+                    yield "absolute_import", (fromlist, names[oparg])
+                else: # relative import
+                    yield "relative_import", (level, fromlist, names[oparg])
+                continue
+
+    def scan_code(self, co, m):
+        code = co.co_code
+        scanner = self.scan_opcodes
+        for what, args in scanner(co):
+            if what == "store":
+                name, = args
+                m.globalnames[name] = 1
+            elif what == "absolute_import":
+                fromlist, name = args
+                have_star = 0
+                if fromlist is not None:
+                    if "*" in fromlist:
+                        have_star = 1
+                    fromlist = [f for f in fromlist if f != "*"]
+                self._safe_import_hook(name, m, fromlist, level=0)
+                if have_star:
+                    # We've encountered an "import *". If it is a Python module,
+                    # the code has already been parsed and we can suck out the
+                    # global names.
+                    mm = None
+                    if m.__path__:
+                        # At this point we don't know whether 'name' is a
+                        # submodule of 'm' or a global module. Let's just try
+                        # the full name first.
+                        mm = self.modules.get(m.__name__ + "." + name)
+                    if mm is None:
+                        mm = self.modules.get(name)
+                    if mm is not None:
+                        m.globalnames.update(mm.globalnames)
+                        m.starimports.update(mm.starimports)
+                        if mm.__code__ is None:
+                            m.starimports[name] = 1
+                    else:
+                        m.starimports[name] = 1
+            elif what == "relative_import":
+                level, fromlist, name = args
+                if name:
+                    self._safe_import_hook(name, m, fromlist, level=level)
+                else:
+                    parent = self.determine_parent(m, level=level)
+                    self._safe_import_hook(parent.__name__, None, fromlist, level=0)
+            else:
+                # We don't expect anything else from the generator.
+                raise RuntimeError(what)
+
+        for c in co.co_consts:
+            if isinstance(c, type(co)):
+                self.scan_code(c, m)
+
+    def load_package(self, fqname, pathname):
+        self.msgin(2, "load_package", fqname, pathname)
+        newname = replacePackageMap.get(fqname)
+        if newname:
+            fqname = newname
+        m = self.add_module(fqname)
+        m.__file__ = pathname
+        m.__path__ = [pathname]
+
+        # As per comment at top of file, simulate runtime __path__ additions.
+        m.__path__ = m.__path__ + packagePathMap.get(fqname, [])
+
+        fp, buf, stuff = self.find_module("__init__", m.__path__)
+        try:
+            self.load_module(fqname, fp, buf, stuff)
+            self.msgout(2, "load_package ->", m)
+            return m
+        finally:
+            if fp:
+                fp.close()
+
+    def add_module(self, fqname):
+        if fqname in self.modules:
+            return self.modules[fqname]
+        self.modules[fqname] = m = Module(fqname)
+        return m
+
+    def find_module(self, name, path, parent=None):
+        if parent is not None:
+            # assert path is not None
+            fullname = parent.__name__+'.'+name
+        else:
+            fullname = name
+        if fullname in self.excludes:
+            self.msgout(3, "find_module -> Excluded", fullname)
+            raise ImportError(name)
+
+        if path is None:
+            if name in sys.builtin_module_names:
+                return (None, None, ("", "", _C_BUILTIN))
+
+            path = self.path
+
+        return _find_module(name, path)
+
+    def report(self):
+        """Print a report to stdout, listing the found modules with their
+        paths, as well as modules that are missing, or seem to be missing.
+        """
+        print()
+        print("  %-25s %s" % ("Name", "File"))
+        print("  %-25s %s" % ("----", "----"))
+        # Print modules found
+        keys = sorted(self.modules.keys())
+        for key in keys:
+            m = self.modules[key]
+            if m.__path__:
+                print("P", end=' ')
+            else:
+                print("m", end=' ')
+            print("%-25s" % key, m.__file__ or "")
+
+        # Print missing modules
+        missing, maybe = self.any_missing_maybe()
+        if missing:
+            print()
+            print("Missing modules:")
+            for name in missing:
+                mods = sorted(self.badmodules[name].keys())
+                print("?", name, "imported from", ', '.join(mods))
+        # Print modules that may be missing, but then again, maybe not...
+        if maybe:
+            print()
+            print("Submodules that appear to be missing, but could also be", end=' ')
+            print("global names in the parent package:")
+            for name in maybe:
+                mods = sorted(self.badmodules[name].keys())
+                print("?", name, "imported from", ', '.join(mods))
+
+    def any_missing(self):
+        """Return a list of modules that appear to be missing. Use
+        any_missing_maybe() if you want to know which modules are
+        certain to be missing, and which *may* be missing.
+        """
+        missing, maybe = self.any_missing_maybe()
+        return missing + maybe
+
+    def any_missing_maybe(self):
+        """Return two lists, one with modules that are certainly missing
+        and one with modules that *may* be missing. The latter names could
+        either be submodules *or* just global names in the package.
+
+        The reason it can't always be determined is that it's impossible to
+        tell which names are imported when "from module import *" is done
+        with an extension module, short of actually importing it.
+        """
+        missing = []
+        maybe = []
+        for name in self.badmodules:
+            if name in self.excludes:
+                continue
+            i = name.rfind(".")
+            if i < 0:
+                missing.append(name)
+                continue
+            subname = name[i+1:]
+            pkgname = name[:i]
+            pkg = self.modules.get(pkgname)
+            if pkg is not None:
+                if pkgname in self.badmodules[name]:
+                    # The package tried to import this module itself and
+                    # failed. It's definitely missing.
+                    missing.append(name)
+                elif subname in pkg.globalnames:
+                    # It's a global in the package: definitely not missing.
+                    pass
+                elif pkg.starimports:
+                    # It could be missing, but the package did an "import *"
+                    # from a non-Python module, so we simply can't be sure.
+                    maybe.append(name)
+                else:
+                    # It's not a global in the package, the package didn't
+                    # do funny star imports, it's very likely to be missing.
+                    # The symbol could be inserted into the package from the
+                    # outside, but since that's not good style we simply list
+                    # it missing.
+                    missing.append(name)
+            else:
+                missing.append(name)
+        missing.sort()
+        maybe.sort()
+        return missing, maybe
+
+    def replace_paths_in_code(self, co):
+        new_filename = original_filename = os.path.normpath(co.co_filename)
+        for f, r in self.replace_paths:
+            if original_filename.startswith(f):
+                new_filename = r + original_filename[len(f):]
+                break
+
+        if self.debug and original_filename not in self.processed_paths:
+            if new_filename != original_filename:
+                self.msgout(2, "co_filename %r changed to %r" \
+                                    % (original_filename,new_filename,))
+            else:
+                self.msgout(2, "co_filename %r remains unchanged" \
+                                    % (original_filename,))
+            self.processed_paths.append(original_filename)
+
+        consts = list(co.co_consts)
+        for i in range(len(consts)):
+            if isinstance(consts[i], type(co)):
+                consts[i] = self.replace_paths_in_code(consts[i])
+
+        return co.replace(co_consts=tuple(consts), co_filename=new_filename)
+
+
+def test():
+    # Parse command line
+    import getopt
+    try:
+        opts, args = getopt.getopt(sys.argv[1:], "dmp:qx:")
+    except getopt.error as msg:
+        print(msg)
+        return
+
+    # Process options
+    debug = 1
+    domods = 0
+    addpath = []
+    exclude = []
+    for o, a in opts:
+        if o == '-d':
+            debug = debug + 1
+        if o == '-m':
+            domods = 1
+        if o == '-p':
+            addpath = addpath + a.split(os.pathsep)
+        if o == '-q':
+            debug = 0
+        if o == '-x':
+            exclude.append(a)
+
+    # Provide default arguments
+    if not args:
+        script = "hello.py"
+    else:
+        script = args[0]
+
+    # Set the path based on sys.path and the script directory
+    path = sys.path[:]
+    path[0] = os.path.dirname(script)
+    path = addpath + path
+    if debug > 1:
+        print("path:")
+        for item in path:
+            print("   ", repr(item))
+
+    # Create the module finder and turn its crank
+    mf = ModuleFinder(path, debug, exclude)
+    for arg in args[1:]:
+        if arg == '-m':
+            domods = 1
+            continue
+        if domods:
+            if arg[-2:] == '.*':
+                mf.import_hook(arg[:-2], None, ["*"])
+            else:
+                mf.import_hook(arg)
+        else:
+            mf.load_file(arg)
+    mf.run_script(script)
+    mf.report()
+    return mf  # for -i debugging
+
+
+if __name__ == '__main__':
+    try:
+        mf = test()
+    except KeyboardInterrupt:
+        print("\n[interrupted]")
diff --git a/Lib/test/test_modulefinder.py b/Lib/test/test_modulefinder.py
new file mode 100644
index 0000000000..ca1058b8d4
--- /dev/null
+++ b/Lib/test/test_modulefinder.py
@@ -0,0 +1,437 @@
+import os
+import errno
+import importlib.machinery
+import py_compile
+import shutil
+import unittest
+import tempfile
+
+from test import support
+
+import modulefinder
+
+TEST_DIR = tempfile.mkdtemp()
+TEST_PATH = [TEST_DIR, os.path.dirname(tempfile.__file__)]
+
+# Each test description is a list of 5 items:
+#
+# 1. a module name that will be imported by modulefinder
+# 2. a list of module names that modulefinder is required to find
+# 3. a list of module names that modulefinder should complain
+#    about because they are not found
+# 4. a list of module names that modulefinder should complain
+#    about because they MAY be not found
+# 5. a string specifying packages to create; the format is obvious imo.
+#
+# Each package will be created in TEST_DIR, and TEST_DIR will be
+# removed after the tests again.
+# Modulefinder searches in a path that contains TEST_DIR, plus
+# the standard Lib directory.
+
+maybe_test = [
+    "a.module",
+    ["a", "a.module", "sys",
+     "b"],
+    ["c"], ["b.something"],
+    """\
+a/__init__.py
+a/module.py
+                                from b import something
+                                from c import something
+b/__init__.py
+                                from sys import *
+""",
+]
+
+maybe_test_new = [
+    "a.module",
+    ["a", "a.module", "sys",
+     "b", "__future__"],
+    ["c"], ["b.something"],
+    """\
+a/__init__.py
+a/module.py
+                                from b import something
+                                from c import something
+b/__init__.py
+                                from __future__ import absolute_import
+                                from sys import *
+"""]
+
+package_test = [
+    "a.module",
+    ["a", "a.b", "a.c", "a.module", "mymodule", "sys"],
+    ["blahblah", "c"], [],
+    """\
+mymodule.py
+a/__init__.py
+                                import blahblah
+                                from a import b
+                                import c
+a/module.py
+                                import sys
+                                from a import b as x
+                                from a.c import sillyname
+a/b.py
+a/c.py
+                                from a.module import x
+                                import mymodule as sillyname
+                                from sys import version_info
+"""]
+
+absolute_import_test = [
+    "a.module",
+    ["a", "a.module",
+     "b", "b.x", "b.y", "b.z",
+     "__future__", "sys", "gc"],
+    ["blahblah", "z"], [],
+    """\
+mymodule.py
+a/__init__.py
+a/module.py
+                                from __future__ import absolute_import
+                                import sys # sys
+                                import blahblah # fails
+                                import gc # gc
+                                import b.x # b.x
+                                from b import y # b.y
+                                from b.z import * # b.z.*
+a/gc.py
+a/sys.py
+                                import mymodule
+a/b/__init__.py
+a/b/x.py
+a/b/y.py
+a/b/z.py
+b/__init__.py
+                                import z
+b/unused.py
+b/x.py
+b/y.py
+b/z.py
+"""]
+
+relative_import_test = [
+    "a.module",
+    ["__future__",
+     "a", "a.module",
+     "a.b", "a.b.y", "a.b.z",
+     "a.b.c", "a.b.c.moduleC",
+     "a.b.c.d", "a.b.c.e",
+     "a.b.x",
+     "gc"],
+    [], [],
+    """\
+mymodule.py
+a/__init__.py
+                                from .b import y, z # a.b.y, a.b.z
+a/module.py
+                                from __future__ import absolute_import # __future__
+                                import gc # gc
+a/gc.py
+a/sys.py
+a/b/__init__.py
+                                from ..b import x # a.b.x
+                                #from a.b.c import moduleC
+                                from .c import moduleC # a.b.moduleC
+a/b/x.py
+a/b/y.py
+a/b/z.py
+a/b/g.py
+a/b/c/__init__.py
+                                from ..c import e # a.b.c.e
+a/b/c/moduleC.py
+                                from ..c import d # a.b.c.d
+a/b/c/d.py
+a/b/c/e.py
+a/b/c/x.py
+"""]
+
+relative_import_test_2 = [
+    "a.module",
+    ["a", "a.module",
+     "a.sys",
+     "a.b", "a.b.y", "a.b.z",
+     "a.b.c", "a.b.c.d",
+     "a.b.c.e",
+     "a.b.c.moduleC",
+     "a.b.c.f",
+     "a.b.x",
+     "a.another"],
+    [], [],
+    """\
+mymodule.py
+a/__init__.py
+                                from . import sys # a.sys
+a/another.py
+a/module.py
+                                from .b import y, z # a.b.y, a.b.z
+a/gc.py
+a/sys.py
+a/b/__init__.py
+                                from .c import moduleC # a.b.c.moduleC
+                                from .c import d # a.b.c.d
+a/b/x.py
+a/b/y.py
+a/b/z.py
+a/b/c/__init__.py
+                                from . import e # a.b.c.e
+a/b/c/moduleC.py
+                                #
+                                from . import f   # a.b.c.f
+                                from .. import x  # a.b.x
+                                from ... import another # a.another
+a/b/c/d.py
+a/b/c/e.py
+a/b/c/f.py
+"""]
+
+relative_import_test_3 = [
+    "a.module",
+    ["a", "a.module"],
+    ["a.bar"],
+    [],
+    """\
+a/__init__.py
+                                def foo(): pass
+a/module.py
+                                from . import foo
+                                from . import bar
+"""]
+
+relative_import_test_4 = [
+    "a.module",
+    ["a", "a.module"],
+    [],
+    [],
+    """\
+a/__init__.py
+                                def foo(): pass
+a/module.py
+                                from . import *
+"""]
+
+bytecode_test = [
+    "a",
+    ["a"],
+    [],
+    [],
+    ""
+]
+
+syntax_error_test = [
+    "a.module",
+    ["a", "a.module", "b"],
+    ["b.module"], [],
+    """\
+a/__init__.py
+a/module.py
+                                import b.module
+b/__init__.py
+b/module.py
+                                ?  # SyntaxError: invalid syntax
+"""]
+
+
+same_name_as_bad_test = [
+    "a.module",
+    ["a", "a.module", "b", "b.c"],
+    ["c"], [],
+    """\
+a/__init__.py
+a/module.py
+                                import c
+                                from b import c
+b/__init__.py
+b/c.py
+"""]
+
+coding_default_utf8_test = [
+    "a_utf8",
+    ["a_utf8", "b_utf8"],
+    [], [],
+    """\
+a_utf8.py
+                                # use the default of utf8
+                                print('Unicode test A code point 2090 \u2090 that is not valid in cp1252')
+                                import b_utf8
+b_utf8.py
+                                # use the default of utf8
+                                print('Unicode test B code point 2090 \u2090 that is not valid in cp1252')
+"""]
+
+coding_explicit_utf8_test = [
+    "a_utf8",
+    ["a_utf8", "b_utf8"],
+    [], [],
+    """\
+a_utf8.py
+                                # coding=utf8
+                                print('Unicode test A code point 2090 \u2090 that is not valid in cp1252')
+                                import b_utf8
+b_utf8.py
+                                # use the default of utf8
+                                print('Unicode test B code point 2090 \u2090 that is not valid in cp1252')
+"""]
+
+coding_explicit_cp1252_test = [
+    "a_cp1252",
+    ["a_cp1252", "b_utf8"],
+    [], [],
+    b"""\
+a_cp1252.py
+                                # coding=cp1252
+                                # 0xe2 is not allowed in utf8
+                                print('CP1252 test P\xe2t\xe9')
+                                import b_utf8
+""" + """\
+b_utf8.py
+                                # use the default of utf8
+                                print('Unicode test A code point 2090 \u2090 that is not valid in cp1252')
+""".encode('utf-8')]
+
+def open_file(path):
+    dirname = os.path.dirname(path)
+    try:
+        os.makedirs(dirname)
+    except OSError as e:
+        if e.errno != errno.EEXIST:
+            raise
+    return open(path, 'wb')
+
+
+def create_package(source):
+    ofi = None
+    try:
+        for line in source.splitlines():
+            if type(line) != bytes:
+                line = line.encode('utf-8')
+            if line.startswith(b' ') or line.startswith(b'\t'):
+                ofi.write(line.strip() + b'\n')
+            else:
+                if ofi:
+                    ofi.close()
+                if type(line) == bytes:
+                    line = line.decode('utf-8')
+                ofi = open_file(os.path.join(TEST_DIR, line.strip()))
+    finally:
+        if ofi:
+            ofi.close()
+
+class ModuleFinderTest(unittest.TestCase):
+    def _do_test(self, info, report=False, debug=0, replace_paths=[], modulefinder_class=modulefinder.ModuleFinder):
+        import_this, modules, missing, maybe_missing, source = info
+        create_package(source)
+        try:
+            mf = modulefinder_class(path=TEST_PATH, debug=debug,
+                                           replace_paths=replace_paths)
+            mf.import_hook(import_this)
+            if report:
+                mf.report()
+##                # This wouldn't work in general when executed several times:
+##                opath = sys.path[:]
+##                sys.path = TEST_PATH
+##                try:
+##                    __import__(import_this)
+##                except:
+##                    import traceback; traceback.print_exc()
+##                sys.path = opath
+##                return
+            modules = sorted(set(modules))
+            found = sorted(mf.modules)
+            # check if we found what we expected, not more, not less
+            self.assertEqual(found, modules)
+
+            # check for missing and maybe missing modules
+            bad, maybe = mf.any_missing_maybe()
+            self.assertEqual(bad, missing)
+            self.assertEqual(maybe, maybe_missing)
+        finally:
+            shutil.rmtree(TEST_DIR)
+
+    def test_package(self):
+        self._do_test(package_test)
+
+    def test_maybe(self):
+        self._do_test(maybe_test)
+
+    def test_maybe_new(self):
+        self._do_test(maybe_test_new)
+
+    def test_absolute_imports(self):
+        self._do_test(absolute_import_test)
+
+    def test_relative_imports(self):
+        self._do_test(relative_import_test)
+
+    def test_relative_imports_2(self):
+        self._do_test(relative_import_test_2)
+
+    def test_relative_imports_3(self):
+        self._do_test(relative_import_test_3)
+
+    def test_relative_imports_4(self):
+        self._do_test(relative_import_test_4)
+
+    def test_syntax_error(self):
+        self._do_test(syntax_error_test)
+
+    def test_same_name_as_bad(self):
+        self._do_test(same_name_as_bad_test)
+
+    def test_bytecode(self):
+        base_path = os.path.join(TEST_DIR, 'a')
+        source_path = base_path + importlib.machinery.SOURCE_SUFFIXES[0]
+        bytecode_path = base_path + importlib.machinery.BYTECODE_SUFFIXES[0]
+        with open_file(source_path) as file:
+            file.write('testing_modulefinder = True\n'.encode('utf-8'))
+        py_compile.compile(source_path, cfile=bytecode_path)
+        os.remove(source_path)
+        self._do_test(bytecode_test)
+
+    def test_replace_paths(self):
+        old_path = os.path.join(TEST_DIR, 'a', 'module.py')
+        new_path = os.path.join(TEST_DIR, 'a', 'spam.py')
+        with support.captured_stdout() as output:
+            self._do_test(maybe_test, debug=2,
+                          replace_paths=[(old_path, new_path)])
+        output = output.getvalue()
+        expected = "co_filename %r changed to %r" % (old_path, new_path)
+        self.assertIn(expected, output)
+
+    def test_extended_opargs(self):
+        extended_opargs_test = [
+            "a",
+            ["a", "b"],
+            [], [],
+            """\
+a.py
+                                %r
+                                import b
+b.py
+""" % list(range(2**16))]  # 2**16 constants
+        self._do_test(extended_opargs_test)
+
+    def test_coding_default_utf8(self):
+        self._do_test(coding_default_utf8_test)
+
+    def test_coding_explicit_utf8(self):
+        self._do_test(coding_explicit_utf8_test)
+
+    def test_coding_explicit_cp1252(self):
+        self._do_test(coding_explicit_cp1252_test)
+
+    def test_load_module_api(self):
+        class CheckLoadModuleApi(modulefinder.ModuleFinder):
+            def __init__(self, *args, **kwds):
+                super().__init__(*args, **kwds)
+
+            def load_module(self, fqname, fp, pathname, file_info):
+                # confirm that the fileinfo is a tuple of 3 elements
+                suffix, mode, type = file_info
+                return super().load_module(fqname, fp, pathname, file_info)
+
+        self._do_test(absolute_import_test, modulefinder_class=CheckLoadModuleApi)
+
+if __name__ == "__main__":
+    unittest.main()