Boy Scout: Create document parser spec file

Regroup DocumentParser spec. Now they're duplicates in
local_census_specs and census_api_spec.

Move duplicate private method "dni?(document_type) from
LocalCensus and CensusAPI to DocumentParser

spec/lib/local_census_spec.rb

@@ -3,30 +3,6 @@ require "rails_helper"
 describe LocalCensus do
   let(:api) { described_class.new }
 
-  describe "#get_document_number_variants" do
-    it "trims and cleans up entry" do
-      expect(api.get_document_number_variants(2, "  1 2@ 34")).to eq(["1234"])
-    end
-
-    it "returns only one try for passports & residence cards" do
-      expect(api.get_document_number_variants(2, "1234")).to eq(["1234"])
-      expect(api.get_document_number_variants(3, "1234")).to eq(["1234"])
-    end
-
-    it "takes only the last 8 digits for dnis and resicence cards" do
-      expect(api.get_document_number_variants(1, "543212345678")).to eq(["12345678"])
-    end
-
-    it "tries all the dni variants padding with zeroes" do
-      expect(api.get_document_number_variants(1, "0123456")).to eq(["123456", "0123456", "00123456"])
-      expect(api.get_document_number_variants(1, "00123456")).to eq(["123456", "0123456", "00123456"])
-    end
-
-    it "adds upper and lowercase letter when the letter is present" do
-      expect(api.get_document_number_variants(1, "1234567A")).to eq(["1234567", "01234567", "1234567a", "1234567A", "01234567a", "01234567A"])
-    end
-  end
-
   describe "#call" do
     let(:invalid_body) { nil }
     let(:valid_body) { create(:local_census_record) }