Add Cycle#notation_extended_by(count)

For most Cycle types this just returns the original notation

lib/sof/cycle.rb

@@ -165,6 +165,8 @@ def ==(other) = to_h == other.to_h
     # Return the most recent completion date from the supplied array of dates
     def last_completed(dates) = dates.compact.map(&:to_date).max
 
+    def notation_extended_by(_ = nil) = notation
+
     # From the supplied anchor date, are there enough in-window completions to
     # satisfy the cycle?
     #

spec/sof/cycles/calendar_spec.rb

@@ -32,6 +32,7 @@ module SOF
     it_behaves_like "it computes #final_date(given)",
       given: "1971-01-01", returns: "1971-12-31".to_date
     it_behaves_like "last_completed is", :recent_date
+    it_behaves_like "it cannot be extended"
 
     describe "#recurring?" do
       it "repeats" do

spec/sof/cycles/end_of_spec.rb

@@ -39,6 +39,7 @@ module SOF
     it_behaves_like "#as_json returns the notation"
     it_behaves_like "it computes #final_date(given)",
       given: nil, returns: ("2020-01-01".to_date + 17.months).end_of_month
+    it_behaves_like "it cannot be extended"
 
     describe "#last_completed" do
       context "with an activated cycle" do

spec/sof/cycles/lookback_spec.rb

@@ -32,6 +32,7 @@ module SOF
     it_behaves_like "it computes #final_date(given)",
       given: "2003-03-08", returns: ("2003-03-08".to_date + 180.days)
     it_behaves_like "last_completed is", :recent_date
+    it_behaves_like "it cannot be extended"
 
     describe "#recurring?" do
       it "repeats" do

spec/sof/cycles/shared_examples.rb

@@ -51,3 +51,9 @@
     expect(subject.last_completed(dates)).to eq(expected)
   end
 end
+
+shared_examples_for "it cannot be extended" do
+  it "returns its original notation" do
+    expect(subject.notation_extended_by(999)).to eq(subject.notation)
+  end
+end

spec/sof/cycles/volume_only_spec.rb

@@ -30,6 +30,7 @@ module SOF
     it_behaves_like "it computes #final_date(given)",
       given: "2003-03-08", returns: nil
     it_behaves_like "last_completed is", :recent_date
+    it_behaves_like "it cannot be extended"
 
     describe "#recurring?" do
       it "does not repeat" do