Add test for heading

Author: robinst

commonmark/src/test/java/org/commonmark/test/TextContentRendererTest.java

@@ -30,6 +30,13 @@ public void textContentText() {
         assertStripped(s, "foo foo bar bar");
     }
 
+    @Test
+    public void textContentHeading() {
+        assertCompact("# Heading\n\nFoo", "Heading\nFoo");
+        assertSeparate("# Heading\n\nFoo", "Heading\n\nFoo");
+        assertStripped("# Heading\n\nFoo", "Heading: Foo");
+    }
+
     @Test
     public void textContentEmphasis() {
         String s;