test: add tests for new changes

spec/brazil_cep/adapters_spec.rb

@@ -1,5 +1,36 @@
+# frozen_string_literal: true
+
 require "spec_helper"
 
 RSpec.describe Brazil::Cep::Adapters do
-  it { expect(1.to_s).to eq("1") }
+  describe ".providers" do
+    it "returns a list of providers" do
+      expect(described_class.providers).to include(
+        viacep: described_class::Viacep,
+        postmon: described_class::Postmon,
+        republica_virtual: described_class::RepublicaVirtual
+      )
+    end
+  end
+
+  describe ".register" do
+    it "registers a provider" do
+      Brazil::Cep::Adapters::CustomProvider = Class.new(Brazil::Cep::Adapters::Base) do
+      end
+
+      described_class.register(:custom_provider, described_class::CustomProvider)
+
+      expect(described_class.providers).to include(custom_provider: described_class::CustomProvider)
+    end
+  end
+
+  describe ".get" do
+    it "returns a default (viacep) provider instance" do
+      expect(described_class.get).to be_a(described_class::Viacep)
+    end
+
+    it { expect(described_class.get(:postmon)).to be_a(described_class::Postmon) }
+
+    it { expect(described_class.get(:republica_virtual)).to be_a(described_class::RepublicaVirtual) }
+  end
 end