diff --git a/Lib/test/test_calendar.py b/Lib/test/test_calendar.py
index 40fb76d..accd16c 100644
--- a/Lib/test/test_calendar.py
+++ b/Lib/test/test_calendar.py
@@ -2,11 +2,22 @@
 import unittest
 
 from test import test_support
+from test.script_helper import assert_python_ok, assert_python_failure
 import locale
 import datetime
+import os
 
+result_2004_01_text = """\
+    January 2004
+Mo Tu We Th Fr Sa Su
+          1  2  3  4
+ 5  6  7  8  9 10 11
+12 13 14 15 16 17 18
+19 20 21 22 23 24 25
+26 27 28 29 30 31
+"""
 
-result_2004_text = """
+result_2004_text = """\
                                   2004
 
       January                   February                   March
@@ -44,7 +55,7 @@
 25 26 27 28 29 30 31      29 30                     27 28 29 30 31
 """
 
-result_2004_html = """
+result_2004_html = """\
 <?xml version="1.0" encoding="ascii"?>
 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
 <html>
@@ -460,6 +471,124 @@
         self.assertEqual(calendar.leapdays(1997,2020), 5)
 
 
+class CommandLineTestCase(unittest.TestCase):
+    def run_ok(self, *args):
+        return assert_python_ok('-m', 'calendar', *args)[1]
+
+    def assertFailure(self, *args):
+        rc, stdout, stderr = assert_python_failure('-m', 'calendar', *args)
+        self.assertIn(b'Usage:', stderr)
+        self.assertEqual(rc, 2)
+
+    def test_help(self):
+        stdout = self.run_ok('-h')
+        self.assertIn(b'Usage:', stdout)
+        self.assertIn(b'calendar.py', stdout)
+        self.assertIn(b'--help', stdout)
+
+    def test_illegal_arguments(self):
+        self.assertFailure('-z')
+        #self.assertFailure('spam')
+        #self.assertFailure('2004', 'spam')
+        self.assertFailure('-t', 'html', '2004', '1')
+
+    def test_output_current_year(self):
+        stdout = self.run_ok()
+        year = datetime.datetime.now().year
+        self.assertIn((' %s' % year).encode(), stdout)
+        self.assertIn(b'January', stdout)
+        self.assertIn(b'Mo Tu We Th Fr Sa Su', stdout)
+
+    def test_output_year(self):
+        stdout = self.run_ok('2004')
+        self.assertEqual(stdout.strip(), result_2004_text.strip())
+
+    def test_output_month(self):
+        stdout = self.run_ok('2004', '1')
+        self.assertEqual(stdout.strip(), result_2004_01_text.strip())
+
+    def test_option_encoding(self):
+        self.assertFailure('-e')
+        self.assertFailure('--encoding')
+        stdout = self.run_ok('--encoding', 'rot-13', '2004')
+        self.assertEqual(stdout.strip(), result_2004_text.encode('rot-13').strip())
+
+    def test_option_locale(self):
+        self.assertFailure('-L')
+        self.assertFailure('--locale')
+        self.assertFailure('-L', 'en')
+        lang, enc = locale.getdefaultlocale()
+        lang = lang or 'C'
+        enc = enc or 'UTF-8'
+        try:
+            oldlocale = locale.getlocale(locale.LC_TIME)
+            try:
+                locale.setlocale(locale.LC_TIME, (lang, enc))
+            finally:
+                locale.setlocale(locale.LC_TIME, oldlocale)
+        except (locale.Error, ValueError):
+            self.skipTest('cannot set the system default locale')
+        stdout = self.run_ok('--locale', lang, '--encoding', enc, '2004')
+        self.assertIn('2004'.encode(enc), stdout)
+
+    def test_option_width(self):
+        self.assertFailure('-w')
+        self.assertFailure('--width')
+        self.assertFailure('-w', 'spam')
+        stdout = self.run_ok('--width', '3', '2004')
+        self.assertIn(b'Mon Tue Wed Thu Fri Sat Sun', stdout)
+
+    def test_option_lines(self):
+        self.assertFailure('-l')
+        self.assertFailure('--lines')
+        self.assertFailure('-l', 'spam')
+        stdout = self.run_ok('--lines', '2', '2004')
+        self.assertIn('December\n\nMo Tu We', stdout)
+
+    def test_option_spacing(self):
+        self.assertFailure('-s')
+        self.assertFailure('--spacing')
+        self.assertFailure('-s', 'spam')
+        stdout = self.run_ok('--spacing', '8', '2004')
+        self.assertIn(b'Su        Mo', stdout)
+
+    def test_option_months(self):
+        self.assertFailure('-m')
+        self.assertFailure('--month')
+        self.assertFailure('-m', 'spam')
+        stdout = self.run_ok('--months', '1', '2004')
+        self.assertIn('\nMo Tu We Th Fr Sa Su\n', stdout)
+
+    def test_option_type(self):
+        self.assertFailure('-t')
+        self.assertFailure('--type')
+        self.assertFailure('-t', 'spam')
+        stdout = self.run_ok('--type', 'text', '2004')
+        self.assertEqual(stdout.strip(), result_2004_text.strip())
+        stdout = self.run_ok('--type', 'html', '2004')
+        self.assertEqual(stdout[:6], b'<?xml ')
+        self.assertIn(b'<title>Calendar for 2004</title>', stdout)
+
+    def test_html_output_current_year(self):
+        stdout = self.run_ok('--type', 'html')
+        year = datetime.datetime.now().year
+        self.assertIn(('<title>Calendar for %s</title>' % year).encode(),
+                      stdout)
+        self.assertIn(b'<tr><th colspan="7" class="month">January</th></tr>',
+                      stdout)
+
+    def test_html_output_year_encoding(self):
+        stdout = self.run_ok('-t', 'html', '--encoding', 'ascii', '2004')
+        self.assertEqual(stdout.strip(), result_2004_html.strip())
+
+    def test_html_output_year_css(self):
+        self.assertFailure('-t', 'html', '-c')
+        self.assertFailure('-t', 'html', '--css')
+        stdout = self.run_ok('-t', 'html', '--css', 'custom.css', '2004')
+        self.assertIn(b'<link rel="stylesheet" type="text/css" '
+                      b'href="custom.css" />', stdout)
+
+
 def test_main():
     test_support.run_unittest(
         OutputTestCase,
@@ -468,8 +597,10 @@
         SundayTestCase,
         MonthRangeTestCase,
         LeapdaysTestCase,
+        CommandLineTestCase,
     )
 
 
 if __name__ == "__main__":
     test_main()
+    unittest.main()
diff --git a/Misc/NEWS b/Misc/NEWS
index 433ce0d..6f02bd4 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -98,6 +98,8 @@
 Tests
 -----
 
+- Issue #18982: Add tests for CLI of the calendar module.
+
 - Issue #19949: The test_xpickle test now tests compatibility with installed
   Python 2.7 and reports skipped tests.  Based on patch by Zachary Ware.