Add tests for GenericTypeRegistry

spec/tapioca/runtime/generic_type_registry_spec.rb

@@ -0,0 +1,103 @@
+# typed: true
+# frozen_string_literal: true
+
+require "spec_helper"
+
+module Tapioca
+  module Runtime
+    class GenericTypeRegistrySpec < Minitest::Spec
+      describe Tapioca::Runtime::GenericTypeRegistry do
+        describe ".generic_type_instance?" do
+          it "returns false for instances of non-generic classes" do
+            refute(GenericTypeRegistry.generic_type_instance?(Object.new))
+          end
+
+          it "returns true for instances of generic classes" do
+            assert(GenericTypeRegistry.generic_type_instance?(SampleGenericClass[Object].new))
+          end
+        end
+
+        describe ".lookup_type_variables" do
+          it "returns nil for non-generic types" do
+            assert_nil(GenericTypeRegistry.lookup_type_variables(Object))
+          end
+
+          it "returns the type variables for generic types" do
+            assert_equal([SampleGenericClass::Element], GenericTypeRegistry.lookup_type_variables(SampleGenericClass))
+          end
+        end
+
+        describe ".register_type_variable" do
+          it " registers a type variable that can be looked up later" do
+            not_actually_generic = Class.new
+
+            fake_type_member1 = Tapioca::TypeVariableModule.new(
+              not_actually_generic,
+              Tapioca::TypeVariableModule::Type::Member,
+              :invariant,
+              nil,
+              nil,
+              nil,
+              nil,
+            )
+
+            fake_type_member2 = Tapioca::TypeVariableModule.new(
+              not_actually_generic,
+              Tapioca::TypeVariableModule::Type::Member,
+              :invariant,
+              nil,
+              nil,
+              nil,
+              nil,
+            )
+
+            GenericTypeRegistry.register_type_variable(not_actually_generic, fake_type_member1)
+            GenericTypeRegistry.register_type_variable(not_actually_generic, fake_type_member2)
+
+            type_variables = T.must(GenericTypeRegistry.lookup_type_variables(not_actually_generic))
+
+            assert_equal([fake_type_member1, fake_type_member2], type_variables)
+            # Let's double-check that they're not just equal, but identical:
+            assert_same(fake_type_member1, type_variables[0])
+            assert_same(fake_type_member2, type_variables[1])
+          end
+        end
+
+        describe "the patch for .inherited on generic classes" do
+          # This is more of an internal detail and cross-cutting concern of all the public APIs,
+          # but it's easier to test here on its own.
+
+          it "rescues exceptions that would prevent subclassing" do
+            assert_raises(RuntimeError) do # Precondition
+              # If not caught by the patch, the error raised from `.inherited` would have blocked our subclassing.
+              Class.new(RaisesInInheritedCallback)
+            end
+
+            result = RaisesInInheritedCallback[Object] # Should be a distinct subclass
+            refute_same(result, RaisesInInheritedCallback)
+            assert_operator(result, :<, RaisesInInheritedCallback)
+          end
+        end
+      end
+
+      class SampleGenericClass
+        extend T::Generic
+
+        Element = type_member
+      end
+
+      class RaisesInInheritedCallback
+        extend T::Generic
+
+        Element = type_member
+
+        class << self
+          def inherited(subclass)
+            super
+            raise "Boom"
+          end
+        end
+      end
+    end
+  end
+end