diff --git a/Lib/idlelib/GrepDialog.py b/Lib/idlelib/GrepDialog.py
index 1d8d51b5932..c0074e24f68 100644
--- a/Lib/idlelib/GrepDialog.py
+++ b/Lib/idlelib/GrepDialog.py
@@ -81,36 +81,24 @@ class GrepDialog(SearchDialogBase):
         hits = 0
         for fn in list:
             try:
-                f = open(fn, errors='replace')
+                with open(fn, errors='replace') as f:
+                    for lineno, line in enumerate(f, 1):
+                        if line[-1:] == '\n':
+                            line = line[:-1]
+                        if prog.search(line):
+                            sys.stdout.write("%s: %s: %s\n" %
+                                             (fn, lineno, line))
+                            hits += 1
             except OSError as msg:
                 print(msg)
-                continue
-            lineno = 0
-            while 1:
-                block = f.readlines(100000)
-                if not block:
-                    break
-                for line in block:
-                    lineno = lineno + 1
-                    if line[-1:] == '\n':
-                        line = line[:-1]
-                    if prog.search(line):
-                        sys.stdout.write("%s: %s: %s\n" % (fn, lineno, line))
-                        hits = hits + 1
-        if hits:
-            if hits == 1:
-                s = ""
-            else:
-                s = "s"
-            print("Found", hits, "hit%s." % s)
-            print("(Hint: right-click to open locations.)")
-        else:
-            print("No hits.")
+        print(("Hits found: %s\n"
+              "(Hint: right-click to open locations.)"
+              % hits) if hits else "No hits.")
 
     def findfiles(self, dir, base, rec):
         try:
             names = os.listdir(dir or os.curdir)
-        except OSError as msg:
+        except OSerror as msg:
             print(msg)
             return []
         list = []
@@ -131,3 +119,9 @@ class GrepDialog(SearchDialogBase):
         if self.top:
             self.top.grab_release()
             self.top.withdraw()
+
+if __name__ == "__main__":
+    # A human test is a bit tricky since EditorWindow() imports this module.
+    # Hence Idle must be restarted after editing this file for a live test.
+    import unittest
+    unittest.main('idlelib.idle_test.test_grep', verbosity=2, exit=False)
diff --git a/Lib/idlelib/idle_test/test_grep.py b/Lib/idlelib/idle_test/test_grep.py
new file mode 100644
index 00000000000..0d8ff0d9f14
--- /dev/null
+++ b/Lib/idlelib/idle_test/test_grep.py
@@ -0,0 +1,80 @@
+""" !Changing this line will break Test_findfile.test_found!
+Non-gui unit tests for idlelib.GrepDialog methods.
+dummy_command calls grep_it calls findfiles.
+An exception raised in one method will fail callers.
+Otherwise, tests are mostly independent.
+*** Currently only test grep_it.
+"""
+import unittest
+from test.support import captured_stdout
+from idlelib.idle_test.mock_tk import Var
+from idlelib.GrepDialog import GrepDialog
+import re
+
+class Dummy_searchengine:
+    '''GrepDialog.__init__ calls parent SearchDiabolBase which attaches the
+    passed in SearchEngine instance as attribute 'engine'. Only a few of the
+    many possible self.engine.x attributes are needed here.
+    '''
+    def getpat(self):
+        return self._pat
+
+searchengine = Dummy_searchengine()
+
+class Dummy_grep:
+    # Methods tested
+    #default_command = GrepDialog.default_command
+    grep_it = GrepDialog.grep_it
+    findfiles = GrepDialog.findfiles
+    # Other stuff needed
+    recvar = Var(False)
+    engine = searchengine
+    def close(self):  # gui method
+        pass
+
+grep = Dummy_grep()
+
+class FindfilesTest(unittest.TestCase):
+    # findfiles is really a function, not a method, could be iterator
+    # test that filename return filename
+    # test that idlelib has many .py files
+    # test that recursive flag adds idle_test .py files
+    pass
+
+class Grep_itTest(unittest.TestCase):
+    # Test captured reports with 0 and some hits.
+    # Should test file names, but Windows reports have mixed / and \ separators
+    # from incomplete replacement, so 'later'.
+
+    def report(self, pat):
+        grep.engine._pat = pat
+        with captured_stdout() as s:
+            grep.grep_it(re.compile(pat), __file__)
+        lines = s.getvalue().split('\n')
+        lines.pop()  # remove bogus '' after last \n
+        return lines
+
+    def test_unfound(self):
+        pat = 'xyz*'*7
+        lines = self.report(pat)
+        self.assertEqual(len(lines), 2)
+        self.assertIn(pat, lines[0])
+        self.assertEqual(lines[1], 'No hits.')
+
+    def test_found(self):
+
+        pat = '""" !Changing this line will break Test_findfile.test_found!'
+        lines = self.report(pat)
+        self.assertEqual(len(lines), 5)
+        self.assertIn(pat, lines[0])
+        self.assertIn('py: 1:', lines[1])  # line number 1
+        self.assertIn('2', lines[3])  # hits found 2
+        self.assertTrue(lines[4].startswith('(Hint:'))
+
+class Default_commandTest(unittest.TestCase):
+    # To write this, mode OutputWindow import to top of GrepDialog
+    # so it can be replaced by captured_stdout in class setup/teardown.
+    pass
+
+if __name__ == '__main__':
+    unittest.main(verbosity=2, exit=False)