Add tests for cache invalidation with ref config and full config

Author: havocp

config/src/test/scala/com/typesafe/config/impl/PublicApiTest.scala

@@ -937,6 +937,28 @@ class PublicApiTest extends TestUtils {
         assertTrue("stuff gets cached repeatedly conf", conf3 eq conf4)
     }
 
+    @Test
+    def invalidateReferenceConfig(): Unit = {
+        val orig = ConfigFactory.defaultReference()
+        val cached = ConfigFactory.defaultReference()
+        assertTrue("reference config was cached", orig eq cached)
+
+        ConfigFactory.invalidateCaches()
+        val changed = ConfigFactory.defaultReference()
+        assertTrue("reference config was invalidated", orig ne changed)
+    }
+
+    @Test
+    def invalidateFullConfig(): Unit = {
+        val orig = ConfigFactory.load()
+        val cached = ConfigFactory.load()
+        assertTrue("full config was cached", orig eq cached)
+
+        ConfigFactory.invalidateCaches()
+        val changed = ConfigFactory.load()
+        assertTrue("full config was invalidated", orig ne changed)
+    }
+
     @Test
     def canUseSomeValuesWithoutResolving(): Unit = {
         val conf = ConfigFactory.parseString("a=42,b=${NOPE}")