Move var helper to its own file

This moves GraphqlHelpers::Var to Graphql::Var and adds specific spec
for it.

spec/support/graphql/var.rb

+# frozen_string_literal: true
+
+module Graphql
+  # Helper to pass variables around generated queries.
+  #
+  # e.g.:
+  #   first = var('Int')
+  #   after = var('String')
+  #
+  #   query = with_signature(
+  #     [first, after],
+  #     query_graphql_path([
+  #       [:project, { full_path: project.full_path }],
+  #       [:issues, { after: after, first: first }]
+  #       :nodes
+  #     ], all_graphql_fields_for('Issue'))
+  #   )
+  #
+  #   post_graphql(query, variables: [first.with(2), after.with(some_cursor)])
+  #
+  class Var
+    attr_reader :name, :type
+    attr_accessor :value
+
+    def initialize(name, type)
+      @name = name
+      @type = type
+    end
+
+    def sig
+      "#{to_graphql_value}: #{type}"
+    end
+
+    def to_graphql_value
+      "$#{name}"
+    end
+
+    # We return a new object so that running the same query twice with
+    # different values does not risk re-using the value
+    #
+    # e.g.
+    #
+    #   x = var('Int')
+    #   expect { post_graphql(query, variables: x) }
+    #     .to issue_same_number_of_queries_as { post_graphql(query, variables: x.with(1)) }
+    #
+    # Here we post the `x` variable once with the value set to 1, and once with
+    # the value set to `nil`.
+    def with(value)
+      copy = Var.new(name, type)
+      copy.value = value
+      copy
+    end
+
+    def to_h
+      { name => value }
+    end
+  end
+end

spec/support/helpers/graphql_helpers.rb

@@ -275,64 +275,8 @@ module GraphqlHelpers
     %Q[query(#{variables.map(&:sig).join(', ')}) #{query}]
   end
 
-  # Helper to pass variables around generated queries.
-  #
-  # e.g.:
-  #   first = var('Int')
-  #   after = var('String')
-  #
-  #   query = with_signature(
-  #     [first, after],
-  #     query_graphql_path([
-  #       [:project, { full_path: project.full_path }],
-  #       [:issues, { after: after, first: first }]
-  #       :nodes
-  #     ], all_graphql_fields_for('Issue'))
-  #   )
-  #
-  #   post_graphql(query, variables: [first.with(2), after.with(some_cursor)])
-  #
-  class Var
-    attr_reader :name, :type
-    attr_accessor :value
-
-    def initialize(name, type)
-      @name = name
-      @type = type
-    end
-
-    def sig
-      "$#{name}: #{type}"
-    end
-
-    def to_graphql_value
-      "$#{name}"
-    end
-
-    # We return a new object so that running the same query twice with
-    # different values does not risk re-using the value
-    #
-    # e.g.
-    #
-    #   x = var('Int')
-    #   expect { post_graphql(query, variables: x) }
-    #     .to issue_same_number_of_queries_as { post_graphql(query, variables: x.with(1)) }
-    #
-    # Here we post the `x` variable once with the value set to 1, and once with
-    # the value set to `nil`.
-    def with(value)
-      copy = Var.new(name, type)
-      copy.value = value
-      copy
-    end
-
-    def to_h
-      { name => value }
-    end
-  end
-
   def var(type)
-    Var.new(generate(:variable), type)
+    ::Graphql::Var.new(generate(:variable), type)
   end
 
   # Fairly dumb Ruby => GraphQL rendering function. Only suitable for testing.

spec/support_specs/graphql/var_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe ::Graphql::Var do
+  subject(:var) { described_class.new('foo', 'Int') }
+
+  it 'associates a name with a type and an initially empty value' do
+    expect(var).to have_attributes(
+      name: 'foo',
+      type: 'Int',
+      value: be_nil
+    )
+  end
+
+  it 'has a correct signature' do
+    expect(var).to have_attributes(sig: '$foo: Int')
+  end
+
+  it 'implements to_graphql_value as $name' do
+    expect(var.to_graphql_value).to eq('$foo')
+  end
+
+  it 'can set a value using with, returning a new object' do
+    with_value = var.with(42)
+
+    expect(with_value).to have_attributes(name: 'foo', type: 'Int', value: 42)
+    expect(var).to have_attributes(value: be_nil)
+  end
+
+  it 'returns an object suitable for passing to post_graphql(variables:)' do
+    expect(var.with(17).to_h).to eq('foo' => 17)
+  end
+end

spec/support_specs/helpers/graphql_helpers_spec.rb

@@ -10,7 +10,7 @@ RSpec.describe GraphqlHelpers do
     query.tr("\n", ' ').gsub(/\s+/, ' ').strip
   end
 
-  describe ::GraphqlHelpers::Var do
+  describe 'var' do
     it 'allocates a fresh name for each var' do
       a = var('Int')
       b = var('Int')