Add specs of snippets from docs

spec/docs/structure_spec.cr

@@ -0,0 +1,34 @@
+require "../spec_helper"
+
+Spectator.describe String do
+  let(normal_string) { "foobar" }
+  let(empty_string) { "" }
+
+  describe "#empty?" do
+    subject { string.empty? }
+
+    context "when empty" do
+      let(string) { empty_string }
+
+      it "is true" do
+        is_expected.to be_true
+      end
+    end
+
+    context "when not empty" do
+      let(string) { normal_string }
+
+      it "is false" do
+        is_expected.to be_false
+      end
+    end
+  end
+end
+
+Spectator.describe Bytes do
+  it "stores an array of bytes" do
+    bytes = Bytes.new(32)
+    bytes[0] = 42
+    expect(bytes[0]).to eq(42)
+  end
+end