Test and fix Version.truncate()

Calling `Version.truncate("build")` should return a fresh instance, as
caught in #141

Closes: #141, #142

3 files changed, 22 insertions, 2 deletions

diff --git a/ChangeLog b/ChangeLog
index d58715d..6c0f593 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -4,7 +4,10 @@ ChangeLog
 2.10.1 (unreleased)
 -------------------
 
-- Nothing changed yet.
+*Bugfix:*
+
+    * `141 <https://github.com/rbarrois/python-semanticversion/issues/141>`_:
+      Ensure we return a new instance for ``Version.truncate("build")``.
 
 
 2.10.0 (2022-05-26)
diff --git a/semantic_version/base.py b/semantic_version/base.py
index 777c27a..1c10155 100644
--- a/semantic_version/base.py
+++ b/semantic_version/base.py
@@ -181,7 +181,14 @@ class Version(object):
     def truncate(self, level='patch'):
         """Return a new Version object, truncated up to the selected level."""
         if level == 'build':
-            return self
+            return Version(
+                major=self.major,
+                minor=self.minor,
+                patch=self.patch,
+                prerelease=self.prerelease,
+                build=self.build,
+                partial=self.partial,
+            )
         elif level == 'prerelease':
             return Version(
                 major=self.major,
diff --git a/tests/test_base.py b/tests/test_base.py
index e6a3733..73d1b08 100755
--- a/tests/test_base.py
+++ b/tests/test_base.py
@@ -395,6 +395,16 @@ class VersionTestCase(unittest.TestCase):
         self.assertEqual(v.prerelease, ())
         self.assertEqual(v.build, ())
 
+    def test_truncate(self):
+        v = base.Version("3.2.1-pre+build")
+        self.assertEqual(v.truncate("build"), v)
+        self.assertIsNot(v.truncate("build"), v)
+        self.assertEqual(v.truncate("prerelease"), base.Version("3.2.1-pre"))
+        self.assertEqual(v.truncate("patch"), base.Version("3.2.1"))
+        self.assertEqual(v.truncate(), base.Version("3.2.1"))
+        self.assertEqual(v.truncate("minor"), base.Version("3.2.0"))
+        self.assertEqual(v.truncate("major"), base.Version("3.0.0"))
+
 
 class SpecItemTestCase(unittest.TestCase):
     if sys.version_info[0] <= 2: