Handle invalid version syntax in pubspecs.

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 47f838a0a7f2fb895a1e9e4f8ac3ce7e6c6748bf..e7608b4cfc375908fd99a6d71b58439d4ac6c997 100644
--- a/sdk/lib/_internal/pub/test/pubspec_test.dart
+++ b/sdk/lib/_internal/pub/test/pubspec_test.dart
@@ -111,10 +111,40 @@ dependencies:
 ''');
     });
 
+    test("throws if dependency version is not a string", () {
+      expectFormatError('''
+dependencies:
+  foo:
+    mock: ok
+    version: 1.2
+''');
+    });
+
+    test("throws if version is not a version constraint", () {
+      expectFormatError('''
+dependencies:
+  foo:
+    mock: ok
+    version: not constraint
+''');
+    });
+
     test("throws if 'name' is not a string", () {
       expectFormatError('name: [not, a, string]');
     });
 
+    test("throws if version is not a string", () {
+      expectFormatError('''
+version: 1.0
+''');
+    });
+
+    test("throws if version is not a version", () {
+      expectFormatError('''
+version: not version
+''');
+    });
+
     test("throws if 'homepage' is not a string", () {
       expectFormatError('homepage:');
       expectFormatError('homepage: [not, a, string]');
@@ -212,6 +242,13 @@ environment:
 ''');
       });
 
+    test("throws if the sdk is not a string", () {
+      expectFormatError('''
+environment:
+  sdk: 1.0
+''');
+    });
+
       test("throws if the sdk isn't a valid version constraint", () {
         expectFormatError('''
 environment: