Add shared examples

spec/support/shared/examples/rex/image_source/image_source.rb

@@ -0,0 +1,23 @@
+shared_examples_for "Rex::ImageSource::ImageSource" do
+
+  describe "#read_asciiz" do
+    let(:offset) { 0 }
+
+    it "returns an String" do
+      expect(subject.read_asciiz(offset)).to be_kind_of(String)
+    end
+
+    it "returns a null free String" do
+      expect(subject.read_asciiz(offset)).to_not include("\x00")
+    end
+
+    context "when offset bigger than available data" do
+      let(:offset) { 12345678 }
+
+      it "returns an empty String" do
+        expect(subject.read_asciiz(offset)).to be_empty
+      end
+    end
+  end
+
+end