Add tests for error_callback

testtools/tests/test_helpers.py

@@ -1,4 +1,4 @@
-# Copyright (c) 2010 testtools developers. See LICENSE for details.
+# Copyright (c) 2010-2011 testtools developers. See LICENSE for details.
 
 from testtools import TestCase
 from testtools.helpers import (
@@ -8,7 +8,35 @@ from testtools.helpers import (
 from testtools.matchers import (
     Equals,
     Is,
+    Not,
     )
+    
+    
+def check_error_callback(test, function, arg, expected_error_count, 
+    expect_result):
+    """General test template for error_callback argument.
+    
+    :param test: Test case instance.
+    :param function: Either try_import or try_imports.
+    :param arg: Name or names to import.
+    :param expected_error_count: Expected number of calls to the callback.
+    :param expect_result: Boolean for whether a module should
+        ultimately be returned or not.
+    """
+    cb_calls = []
+    def cb(e):
+        test.assertIsInstance(e, ImportError)
+        cb_calls.append(e)
+    try:
+        result = function(arg, error_callback=cb)
+    except ImportError, e:
+        test.assertFalse(expect_result)
+    else:
+        if expect_result:
+            test.assertThat(result, Not(Is(None)))
+        else:
+            test.assertThat(result, Is(None))
+    test.assertEquals(len(cb_calls), expected_error_count)
 
 
 class TestTryImport(TestCase):
@@ -51,7 +79,20 @@ class TestTryImport(TestCase):
         result = try_import('os.path.join')
         import os
         self.assertThat(result, Is(os.path.join))
+        
+    def test_error_callback(self):
+        # the error callback is called on failures.
+        check_error_callback(self, try_import, 'doesntexist', 1, False)
 
+    def test_error_callback_missing_module_member(self):
+        # the error callback is called on failures to find an object 
+        # inside an existing module.
+        check_error_callback(self, try_import, 'os.nonexistent', 1, False)
+
+    def test_error_callback_not_on_success(self):
+        # the error callback is not called on success.
+        check_error_callback(self, try_import, 'os.path', 0, True)
+        
 
 class TestTryImports(TestCase):
 
@@ -99,6 +140,18 @@ class TestTryImports(TestCase):
         result = try_imports(['os.doesntexist', 'os.path'])
         import os
         self.assertThat(result, Is(os.path))
+        
+    def test_error_callback(self):
+        # One error for every class that doesn't exist.
+        check_error_callback(self, try_imports, 
+            ['os.doesntexist', 'os.notthiseither'],
+            2, False)
+        check_error_callback(self, try_imports, 
+            ['os.doesntexist', 'os.notthiseither', 'os'],
+            2, True)
+        check_error_callback(self, try_imports, 
+            ['os.path'],
+            0, True)
 
 
 def test_suite():