Add specs for Disk#read and Disk#index

spec/lib/rex/image_source/disk_spec.rb

@@ -13,23 +13,111 @@ describe Rex::ImageSource::Disk do
     File.new(path)
   end
 
+  subject do
+    described_class.new(file)
+  end
+
   describe "#initialize" do
     subject(:disk_class) do
       described_class.allocate
     end
 
+    context "when _len not send as argument" do
+      let(:_file) { file }
+
+      it "initializes size to file length" do
+        disk_class.send(:initialize, file)
+        expect(disk_class.size).to eq(4608)
+      end
+    end
+
+    context "when _offset not send argument" do
+      let(:_file) { file }
+      it "initializes file_offset to 0" do
+        disk_class.send(:initialize, file)
+        expect(disk_class.file_offset).to eq(0)
+      end
+    end
   end
 
   describe "#read" do
-    context "offset minor than 0" do
+    context "when offset minor than 0" do
       let(:offset) { -1 }
       let(:len) { 20 }
+
+      it "raises a RangeError" do
+        expect { subject.read(offset, len) }.to raise_error(RangeError)
+      end
     end
 
+    context "when offset plus len major than size" do
+      let(:offset) { 0 }
+      let(:len) { 16000 }
+
+      it "raises a RangeError" do
+        expect { subject.read(offset, len) }.to raise_error(RangeError)
+      end
+    end
+
+    context "when offset and len inside range" do
+      let(:offset) { 0 }
+      let(:len) { 2 }
+
+      it "returns file contents" do
+        expect(subject.read(offset, len)). to eq('MZ')
+      end
+    end
+
+    context "instance with tampered size" do
+      let(:tampered_size) { 6000 }
+
+      subject(:tampered) do
+        described_class.new(file, 0, tampered_size)
+      end
+
+      context "when reading offset after the real file length" do
+        let(:offset) { 5000 }
+        let(:len) { 2 }
+        it "returns nil" do
+          expect(tampered.read(offset, len)).to be_nil
+        end
+      end
+    end
   end
 
   describe "#index" do
+    let(:search) { 'MZ' }
 
+    it "returns index of first search occurrence" do
+      expect(subject.index(search)).to eq(0)
+    end
+
+    context "when offset out of range" do
+      it "returns nil" do
+        expect(subject.index(search, 6000)).to be_nil
+      end
+    end
+
+    context "when search string not found" do
+      it "returns nil" do
+        expect(subject.index(search, 4600)).to be_nil
+      end
+    end
+
+    context "instance with tampered size" do
+      let(:tampered_size) { 6000 }
+
+      subject(:tampered) do
+        described_class.new(file, 0, tampered_size)
+      end
+
+      context "when searching offset after the real file length" do
+        let(:offset) { 5000 }
+        it "raises NoMethodError" do
+          expect{ tampered.index(search, offset) }.to raise_error(NoMethodError)
+        end
+      end
+    end
   end
 
   describe "#subsource" do
@@ -39,5 +127,4 @@ describe Rex::ImageSource::Disk do
   describe "#close" do
 
   end
-
 end