Add a test for $idx and $len inside nested sections.

js/test_cases/idx_and_len_nested/array.json

@@ -0,0 +1,16 @@
+{
+  "things": [
+    [
+      "Alice",
+      "Andy"
+    ],
+    [
+      "Bob",
+      "Becky"
+    ],
+    [
+      "Chris",
+      "Cathy"
+    ]
+  ]
+}

js/test_cases/idx_and_len_nested/main.dust

@@ -0,0 +1,17 @@
+Outside $idx: {$idx}{~n}
+Outside $len: {$len}{~n}
+Outside {?$idx}$idx is true{:else}$idx is false{/$idx}{~n}
+Outside {?$len}$len is true{:else}$len is false{/$len}{~n}
+
+{#things}
+    Inside Section $idx: {$idx}{~n}
+    Inside Section $len: {$len}{~n}
+    Inside Section {?$idx}$idx is true{:else}$idx is false{/$idx}{~n}
+    Inside Section {?$len}$len is true{:else}$len is false{/$len}{~n}
+    {#.}
+        Inside Nested Section $idx: {$idx}{~n}
+        Inside Nested Section $len: {$len}{~n}
+        Inside Nested Section {?$idx}$idx is true{:else}$idx is false{/$idx}{~n}
+        Inside Nested Section {?$len}$len is true{:else}$len is false{/$len}{~n}
+    {/.}
+{/things}