feature: tag tests; choose tags on command line

test/backend/metadata_test.dart

Index: test/backend/metadata_test.dart
diff --git a/test/backend/metadata_test.dart b/test/backend/metadata_test.dart
index ab14a74bde550a52a9b895f5b73e4085b75c0a37..44156feb9eaa60803c800899d6fb0aa888a6b2cc 100644
--- a/test/backend/metadata_test.dart
+++ b/test/backend/metadata_test.dart
@@ -9,6 +9,91 @@ import 'package:test/src/frontend/skip.dart';
 import 'package:test/test.dart';
 
 void main() {
+  group("Metadata", () {
+    expectTags(tags, expected) {
+      expect(new Metadata(tags: tags).tags, unorderedEquals(expected));
+      expect(new Metadata.parse(tags: tags).tags, unorderedEquals(expected));
+      var serialized = {
+        "tags": tags,
+        "timeout": "none",
+        "onPlatform": [],
+      };
+      expect(new Metadata.deserialize(serialized).tags,
+          unorderedEquals(expected));
+    }
+
+    expectTagsError({tags, String message}) {
+      [
+        () => new Metadata(tags: tags),
+        () => new Metadata.parse(tags: tags),
+      ].forEach((fn()) {
+        try {
+          fn();
+          fail("Expected ArgumentError for $tags");
+        } on ArgumentError catch(e) {
+          expect(e.message, message);
+          expect(e.invalidValue, tags);
+          expect(e.name, "tags");
+        }
+      });
+    }
+
+    test("takes no tags", () {
+      expectTags(null, []);
+      expectTags("", []);
+      expectTags(" ", []);
+      expectTags([], []);
+    });
+
+    test("takes some tags as Iterable", () {
+      var tags = ["a", "b"];
+      expectTags(tags, tags);
+      expectTags(new Set.from(tags), tags);
+    });
+
+    test("takes some tags as String", () {
+      expectTags("a", ["a"]);
+      expectTags("a,b", ["a", "b"]);
+      expectTags(" a,,,b , c\n,d\t", ["a", "b", "c", "d"]);
+    });
+
+    test("refuses bad tag types", () {
+      expectTagsError(
+          tags: 1,
+          message: "must be either String or Iterable");
+    });
+
+    test("refuses non-String tag names", () {
+      expectTagsError(
+          tags: [1],
+          message: "tag name must be String");
+      expectTagsError(
+          tags: [null],
+          message: "tag name must be String");
+    });
+
+    test("refuses blank tag names", () {
+      var errorMsg = "tag name must contain non-whitespace characters";
+      expectTagsError(
+          tags: [""],
+          message: errorMsg);
+      expectTagsError(
+          tags: [" "],
+          message: errorMsg);
+    });
+
+    test("merges tags by computing the union of the two tag sets", () {
+      expect(new Metadata(tags: "a,b").merge(new Metadata(tags: "b,c")).tags,
+        unorderedEquals(["a", "b", "c"]));
+    });
+
+    test("serializes tags to a List", () {
+      var serialized = new Metadata(tags: "a,b").serialize()['tags'];
+      expect(serialized, new isInstanceOf<List>());
+      expect(serialized, ["a", "b"]);
+    });
+  });
+
   group("onPlatform", () {
     test("parses a valid map", () {
       var metadata = new Metadata.parse(onPlatform: {