Add tests

Check for the following:
- Tap migration rename to core tap can be loaded by short name
- Tap migration rename to core tap can be loaded by long name
- Tap migration renam that clashes with existing core tap short name
  is ignored in favor of loading the cask/formula from the core tap

Library/Homebrew/test/cask/cask_loader/from_api_loader_spec.rb

@@ -14,12 +14,14 @@ RSpec.describe Cask::CaskLoader::FromAPILoader, :cask do
 
     before do
       allow(Homebrew::API::Cask)
-        .to receive(:all_casks)
+        .to receive_messages(all_casks: casks_from_api_hash, all_renames: {})
-        .and_return(casks_from_api_hash)
+
+      # The call to `Cask::CaskLoader.load` above sets the Tap cache prematurely.
+      Tap.clear_cache
     end
   end
 
-  describe ".can_load?" do
+  describe ".try_new" do
     include_context "with API setup", "test-opera"
 
     context "when not using the API", :no_api do
@@ -34,16 +36,64 @@ RSpec.describe Cask::CaskLoader::FromAPILoader, :cask do
       end
 
       it "returns a loader for valid token" do
-        expect(described_class.try_new(token)).not_to be_nil
+        expect(described_class.try_new(token))
+          .to be_a(described_class)
+          .and have_attributes(token:)
       end
 
       it "returns a loader for valid full name" do
-        expect(described_class.try_new("homebrew/cask/#{token}")).not_to be_nil
+        expect(described_class.try_new("homebrew/cask/#{token}"))
+          .to be_a(described_class)
+          .and have_attributes(token:)
       end
 
       it "returns nil for full name with invalid tap" do
         expect(described_class.try_new("homebrew/foo/#{token}")).to be_nil
       end
+
+      context "with core tap migration renames" do
+        let(:foo_tap) { Tap.fetch("homebrew", "foo") }
+
+        before do
+          foo_tap.path.mkpath
+        end
+
+        after do
+          FileUtils.rm_rf foo_tap.path
+        end
+
+        it "returns the core cask if the short name clashes with a tap migration rename" do
+          (foo_tap.path/"tap_migrations.json").write <<~JSON
+            { "#{token}": "homebrew/cask/#{token}-v2" }
+          JSON
+
+          expect(Cask::CaskLoader::FromNameLoader.try_new(token))
+            .to be_a(Cask::CaskLoader::FromNameLoader)
+            .and have_attributes(token:)
+        end
+
+        it "returns the tap migration rename by old token" do
+          old_token = "#{token}-old"
+          (foo_tap.path/"tap_migrations.json").write <<~JSON
+            { "#{old_token}": "homebrew/cask/#{token}" }
+          JSON
+
+          expect(Cask::CaskLoader::FromNameLoader.try_new(old_token))
+            .to be_a(described_class)
+            .and have_attributes(token:)
+        end
+
+        it "returns the tap migration rename by old full name" do
+          old_token = "#{token}-old"
+          (foo_tap.path/"tap_migrations.json").write <<~JSON
+            { "#{old_token}": "homebrew/cask/#{token}" }
+          JSON
+
+          expect(Cask::CaskLoader::FromTapLoader.try_new("#{foo_tap}/#{old_token}"))
+            .to be_a(described_class)
+            .and have_attributes(token:)
+        end
+      end
     end
   end
 

Library/Homebrew/test/formulary_spec.rb

@@ -383,6 +383,7 @@ RSpec.describe Formulary do
         # avoid unnecessary network calls
         allow(Homebrew::API::Formula).to receive_messages(all_aliases: {}, all_renames: {})
         allow(CoreTap.instance).to receive(:tap_migrations).and_return({})
+        allow(CoreCaskTap.instance).to receive(:tap_migrations).and_return({})
 
         # don't try to load/fetch gcc/glibc
         allow(DevelopmentTools).to receive_messages(needs_libc_formula?: false, needs_compiler_formula?: false)
@@ -482,6 +483,51 @@ RSpec.describe Formulary do
         expect(formula.deps.count).to eq 5
         expect(formula.deps.map(&:name).include?("uses_from_macos_dep")).to be true
       end
+
+      context "with core tap migration renames" do
+        let(:foo_tap) { Tap.fetch("homebrew", "foo") }
+
+        before do
+          allow(Homebrew::API::Formula).to receive(:all_formulae).and_return formula_json_contents
+          foo_tap.path.mkpath
+        end
+
+        after do
+          FileUtils.rm_rf foo_tap.path
+        end
+
+        it "returns the core formula if the short name clashes with a tap migration rename" do
+          (foo_tap.path/"tap_migrations.json").write <<~JSON
+            { "#{formula_name}": "homebrew/core/#{formula_name}-v2" }
+          JSON
+
+          expect(described_class::FromNameLoader.try_new(formula_name))
+            .to be_a(described_class::FromNameLoader)
+            .and have_attributes(name: formula_name)
+        end
+
+        it "returns the tap migration rename by old formula_name" do
+          old_formula_name = "#{formula_name}-old"
+          (foo_tap.path/"tap_migrations.json").write <<~JSON
+            { "#{old_formula_name}": "homebrew/core/#{formula_name}" }
+          JSON
+
+          expect(described_class::FromNameLoader.try_new(old_formula_name))
+            .to be_a(described_class::FromAPILoader)
+            .and have_attributes(name: formula_name)
+        end
+
+        it "returns the tap migration rename by old full name" do
+          old_formula_name = "#{formula_name}-old"
+          (foo_tap.path/"tap_migrations.json").write <<~JSON
+            { "#{old_formula_name}": "homebrew/core/#{formula_name}" }
+          JSON
+
+          expect(described_class::FromTapLoader.try_new("#{foo_tap}/#{old_formula_name}"))
+            .to be_a(described_class::FromAPILoader)
+            .and have_attributes(name: formula_name)
+        end
+      end
     end
   end