New Rule: Lint/DuplicatedRequire

closes https://github.com/crystal-ameba/ameba/issues/176

spec/ameba/ast/visitors/top_level_nodes_visitor_spec.cr

@@ -0,0 +1,17 @@
+require "../../../spec_helper"
+
+module Ameba::AST
+  describe TopLevelNodesVisitor do
+    describe "#require_nodes" do
+      it "returns require node" do
+        source = Source.new %(
+          require "foo"
+          def bar; end
+        )
+        visitor = TopLevelNodesVisitor.new(source.ast)
+        visitor.require_nodes.size.should eq 1
+        visitor.require_nodes.first.to_s.should eq %q(require "foo")
+      end
+    end
+  end
+end