Add tests and improve docs for Version.primary (dart-lang/pub_semver#47)

pkgs/pub_semver/CHANGELOG.md

diff --git a/pkgs/pub_semver/CHANGELOG.md b/pkgs/pub_semver/CHANGELOG.md
index 40f7c3e..63f7285 100644
--- a/pkgs/pub_semver/CHANGELOG.md
+++ b/pkgs/pub_semver/CHANGELOG.md
@@ -1,3 +1,5 @@
+# 1.4.5-dev
+
 # 1.4.4
 
 - Fix a bug of `VersionRange.union` where ranges bounded at infinity would get

pkgs/pub_semver/lib/src/version.dart

diff --git a/pkgs/pub_semver/lib/src/version.dart b/pkgs/pub_semver/lib/src/version.dart
index e769dcd..314937d 100644
--- a/pkgs/pub_semver/lib/src/version.dart
+++ b/pkgs/pub_semver/lib/src/version.dart
@@ -131,10 +131,12 @@
     }
   }
 
-  /// Returns the primary version out of a list of candidates.
+  /// Returns the primary version out of [versions].
   ///
   /// This is the highest-numbered stable (non-prerelease) version. If there
   /// are no stable versions, it's just the highest-numbered version.
+  ///
+  /// If [versions] is empty, returns `null`.
   static Version primary(List<Version> versions) {
     Version primary;
     for (var version in versions) {

pkgs/pub_semver/pubspec.yaml

diff --git a/pkgs/pub_semver/pubspec.yaml b/pkgs/pub_semver/pubspec.yaml
index a2238d2..78de107 100644
--- a/pkgs/pub_semver/pubspec.yaml
+++ b/pkgs/pub_semver/pubspec.yaml
@@ -1,5 +1,5 @@
 name: pub_semver
-version: 1.4.4
+version: 1.4.5-dev
 
 description: >-
  Versions and version constraints implementing pub's versioning policy. This

pkgs/pub_semver/test/version_test.dart

diff --git a/pkgs/pub_semver/test/version_test.dart b/pkgs/pub_semver/test/version_test.dart
index df0d25b..70d2779 100644
--- a/pkgs/pub_semver/test/version_test.dart
+++ b/pkgs/pub_semver/test/version_test.dart
@@ -2,9 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:test/test.dart';
-
 import 'package:pub_semver/pub_semver.dart';
+import 'package:test/test.dart';
 
 import 'utils.dart';
 
@@ -330,4 +329,55 @@
           equals('001.02.0003-01.dev+pre.002'));
     });
   });
+
+  group('primary', () {
+    test('single', () {
+      expect(
+        _primary([
+          '1.2.3',
+        ]).toString(),
+        '1.2.3',
+      );
+    });
+
+    test('normal', () {
+      expect(
+        _primary([
+          '1.2.3',
+          '1.2.2',
+        ]).toString(),
+        '1.2.3',
+      );
+    });
+
+    test('all prerelease', () {
+      expect(
+        _primary([
+          '1.2.2-dev.1',
+          '1.2.2-dev.2',
+        ]).toString(),
+        '1.2.2-dev.2',
+      );
+    });
+
+    test('later prerelease', () {
+      expect(
+        _primary([
+          '1.2.3',
+          '1.2.3-dev',
+        ]).toString(),
+        '1.2.3',
+      );
+    });
+
+    test('empty', () {
+      expect(
+        _primary([]),
+        isNull,
+      );
+    });
+  });
 }
+
+Version _primary(List<String> input) =>
+    Version.primary(input.map((e) => Version.parse(e)).toList());