api: make BasicTag.convert public

spectator-api/src/main/java/com/netflix/spectator/api/BasicTag.java

@@ -28,7 +28,7 @@ public final class BasicTag implements Tag {
    * implementations will likely vary the hashCode/equals causing ids that should
    * be equivalent to not match as expected.
    */
-  static BasicTag convert(Tag t) {
+  public static BasicTag convert(Tag t) {
     return (t instanceof BasicTag) ? (BasicTag) t : new BasicTag(t.key(), t.value());
   }
 

spectator-api/src/test/java/com/netflix/spectator/api/BasicTagTest.java

@@ -80,4 +80,22 @@ public void testNullValue() {
         NullPointerException.class, () -> new BasicTag("k", null));
     Assertions.assertEquals("parameter 'value' cannot be null (key=k)", e.getMessage());
   }
+
+  @Test
+  public void convertBasicTagReturnsSameInstance() {
+    BasicTag tag = new BasicTag("k", "v");
+    Assertions.assertSame(tag, BasicTag.convert(tag));
+  }
+
+  @Test
+  public void convertNonBasicTag() {
+    Tag tag = new Tag() {
+      @Override public String key() { return "k"; }
+      @Override public String value() { return "v"; }
+    };
+    BasicTag result = BasicTag.convert(tag);
+    Assertions.assertEquals("k", result.key());
+    Assertions.assertEquals("v", result.value());
+    Assertions.assertEquals(new BasicTag("k", "v"), result);
+  }
 }