json: Improve error handling and adding ability to limit log output.

recipe_engine/unittests/util_test.py

 #!/usr/bin/env python
 # Copyright 2015 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
 import unittest
 
 import test_env
 
 from recipe_engine import util
@@ skipping 69 matching lines @@
     self.assertEqual(v, [1, 2, 3])
     self.assertIsNotNone(mexc)
     self.assertEqual(len(mexc), 5)
 
   def testCatchesSpecificExceptions(self):
     def fn(e):
       raise ValueError('Zero')
     self.assertRaises(ValueError, util.map_defer_exceptions, fn, [1], KeyError)
 
 
+class TestSnipOutputLines(unittest.TestCase):
+
+  def testIdempotentOnSmallData(self):
+    small_data = [
+        [''],
+        ['', ''],
+        [' '],
+        [' ', ' '],
+        ['hello world'],
+        ['hello world', ''],
+        ['hello', 'world'],
+        ['', 'hello world'],
+    ]
+
+    for d in small_data:
+      self.assertEqual(d, util.snip_output_lines(d, max_bytes=100))
+
+  def testSnipWithNoLines(self):
+    lines = ['---------']
+    expected = ['--- ...', '<snip>', '... ---']
+    self.assertEqual(
+        expected, util.snip_output_lines(lines, max_bytes=6))
+
+  def testSnipWithLines(self):
+    lines = ['-', '--', '--', '---', '-', '--']
+    expected = ['-', '--', '<snip>', '-' '--']
+    self.assertEqual(
+        expected, util.snip_output_lines(lines, max_bytes=6))
+
+  def testSnipWithLines(self):
+    lines = ['----', '----', '----']
+    expected = ['--- ...', '<snip>', '... ---']
+    self.assertEqual(
+        expected, util.snip_output_lines(lines, max_bytes=6))
+
+  def testExactlyEqual(self):
+    lines = ['---', '---']
+    expected = ['---', '---']
+    self.assertEqual(
+        expected, util.snip_output_lines(lines, max_bytes=6))
+
+
 if __name__ == '__main__':
   unittest.main()