Add specs of snippets from docs

spec/docs/helper_methods_spec.cr

@@ -0,0 +1,57 @@
+Spectator.describe String do
+  # This is a helper method.
+  def random_string(length)
+    chars = ('a'..'z').to_a
+    String.build(length) do |builder|
+      length.times { builder << chars.sample }
+    end
+  end
+
+  describe "#size" do
+    subject { random_string(10).size }
+
+    it "is the length of the string" do
+      is_expected.to eq(10)
+    end
+  end
+end
+Spectator.describe String do
+  # length is now pulled from value defined by `let`.
+  def random_string
+    chars = ('a'..'z').to_a
+    String.build(length) do |builder|
+      length.times { builder << chars.sample }
+    end
+  end
+
+  describe "#size" do
+    let(length) { 10 } # random_string uses this.
+    subject { random_string.size }
+
+    it "is the length of the string" do
+      is_expected.to eq(length)
+    end
+  end
+end
+
+module StringHelpers
+  def random_string
+    chars = ('a'..'z').to_a
+    String.build(length) do |builder|
+      length.times { builder << chars.sample }
+    end
+  end
+end
+
+Spectator.describe String do
+  include StringHelpers
+
+  describe "#size" do
+    let(length) { 10 }
+    subject { random_string.size }
+
+    it "is the length of the string" do
+      is_expected.to eq(length)
+    end
+  end
+end