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

spec/ameba/rule/lint/duplicated_require_spec.cr

@@ -0,0 +1,48 @@
+require "../../../spec_helper"
+
+module Ameba::Rule::Lint
+  subject = DuplicatedRequire.new
+
+  describe DuplicatedRequire do
+    it "passes if there are no duplicated requires" do
+      source = Source.new %(
+        require "math"
+        require "big"
+        require "big/big_decimal"
+      )
+      subject.catch(source).should be_valid
+    end
+
+    it "reports if there are a duplicated requires" do
+      source = Source.new %(
+        require "big"
+        require "math"
+        require "big"
+      )
+      subject.catch(source).should_not be_valid
+    end
+
+    it "reports rule, pos and message" do
+      source = Source.new %(
+        require "./thing"
+        require "./thing"
+        require "./another_thing"
+        require "./another_thing"
+      ), "source.cr"
+
+      subject.catch(source).should_not be_valid
+
+      issue = source.issues.first
+      issue.rule.should_not be_nil
+      issue.location.to_s.should eq "source.cr:2:1"
+      issue.end_location.to_s.should eq ""
+      issue.message.should eq "Duplicated require of `./thing`"
+
+      issue = source.issues.last
+      issue.rule.should_not be_nil
+      issue.location.to_s.should eq "source.cr:4:1"
+      issue.end_location.to_s.should eq ""
+      issue.message.should eq "Duplicated require of `./another_thing`"
+    end
+  end
+end