Printing a useful error message if a version field is a num

sdk/lib/_internal/pub/test/pubspec_test.dart

Index: sdk/lib/_internal/pub/test/pubspec_test.dart
diff --git a/sdk/lib/_internal/pub/test/pubspec_test.dart b/sdk/lib/_internal/pub/test/pubspec_test.dart
index 67f927662497d1cd6b022ef68835ed4e39c867e7..542961df9e28dd79bcd977abd6e9978819652e35 100644
--- a/sdk/lib/_internal/pub/test/pubspec_test.dart
+++ b/sdk/lib/_internal/pub/test/pubspec_test.dart
@@ -231,7 +231,23 @@ dependencies:
     });
 
     test("throws if version is not a string", () {
-      expectPubspecException('version: 1.0', (pubspec) => pubspec.version);
+      expectPubspecException('version: [2, 0, 0]',
+          (pubspec) => pubspec.version,
+          '"version" field must be a string');
+    });
+
+    test("throws if version is malformed (looking like a double)", () {
+      expectPubspecException('version: 2.1',
+          (pubspec) => pubspec.version,
+          '"version" field must have three numeric components: major, minor, '
+          'and patch. Instead of "2.1", consider "2.1.0"');
+    });
+
+    test("throws if version is malformed (looking like an int)", () {
+      expectPubspecException('version: 2',
+          (pubspec) => pubspec.version,
+          '"version" field must have three numeric components: major, minor, '
+          'and patch. Instead of "2", consider "2.0.0"');
     });
 
     test("throws if version is not a version", () {