feat: add ArgumentSet#has? to say if an argument set has a value

lib/rapid/argument_set.rb

@@ -109,6 +109,14 @@ def to_hash
       end
     end
 
+    # Return whether an argument has been provided or not?
+    #
+    # @param name [Symbol]
+    # @return [Boolean]
+    def has?(key)
+      @source.key?(key.to_sym)
+    end
+
     # Validate an argument set and return any errors as appropriate
     #
     # @param argument [Rapid::Argument]

spec/specs/rapid/argument_set_spec.rb

@@ -342,6 +342,41 @@
     end
   end
 
+  context '#has?' do
+    it 'returns false when the argument has not been provided' do
+      as = Rapid::ArgumentSet.create('ExampleSet') do
+        argument :name, type: :string
+      end
+      instance = as.new({})
+      expect(instance.has?(:name)).to be false
+    end
+
+    it 'returns false for values that are provided but are not valid' do
+      as = Rapid::ArgumentSet.create('ExampleSet') do
+        argument :name, type: :string
+      end
+      instance = as.new({ age: 10 })
+      expect(instance.has?(:age)).to be false
+    end
+
+    it 'returns true when the argument has been provided but is nil' do
+      as = Rapid::ArgumentSet.create('ExampleSet') do
+        argument :name, type: :string
+      end
+      instance = as.new({ name: nil })
+      expect(instance.has?(:name)).to be true
+    end
+
+    it 'returns true when the argument has been provided' do
+      as = Rapid::ArgumentSet.create('ExampleSet') do
+        argument :name, type: :string
+      end
+      instance = as.new({ name: 'Dave' })
+      expect(instance.has?(:name)).to be true
+      expect(instance.has?('name')).to be true
+    end
+  end
+
   context '#to_hash' do
     it 'should return a hash of the values' do
       as = Rapid::ArgumentSet.create('ExampleSet') do