1 files changed, 97 insertions, 0 deletions
diff --git a/spec/ruby/core/gc/config_spec.rb b/spec/ruby/core/gc/config_spec.rb
new file mode 100644
index 0000000000..57160f122c
--- /dev/null
+++ b/spec/ruby/core/gc/config_spec.rb
@@ -0,0 +1,97 @@
+require_relative '../../spec_helper'
+
+ruby_version_is "3.4" do
+  describe "GC.config" do
+    context "without arguments" do
+      it "returns a hash of current settings" do
+        GC.config.should.is_a?(Hash)
+      end
+
+      it "includes the name of currently loaded GC implementation as a global key" do
+        GC.config.should.include?(:implementation)
+        GC.config[:implementation].should.is_a?(String)
+      end
+    end
+
+    context "with a hash of options" do
+      it "allows to set GC implementation's options, returning the new config" do
+        config = GC.config({})
+        # Try to find a boolean setting to reliably test changing it.
+        key, _value = config.find { |_k, v| v == true }
+        skip unless key
+
+        GC.config(key => false).should == config.merge(key => false)
+        GC.config[key].should == false
+        GC.config(key => true).should == config
+        GC.config[key].should == true
+      ensure
+        GC.config(config.except(:implementation))
+      end
+
+      it "does not change settings that aren't present in the hash" do
+        previous = GC.config
+        GC.config({})
+        GC.config.should == previous
+      end
+
+      it "ignores unknown keys" do
+        previous = GC.config
+        GC.config(foo: "bar")
+        GC.config.should == previous
+      end
+
+      ruby_version_is ""..."4.0" do
+        it "returns the same as GC.config but without the :implementation key" do
+          previous = GC.config
+          GC.config({}).should == previous.except(:implementation)
+        end
+      end
+
+      ruby_version_is "4.0" do
+        it "returns the same as GC.config, including the :implementation key" do
+          previous = GC.config
+          GC.config({}).should == previous
+        end
+      end
+
+      it "raises an ArgumentError if options include global keys" do
+        -> { GC.config(implementation: "default") }.should.raise(ArgumentError, 'Attempting to set read-only key "Implementation"')
+      end
+    end
+
+    context "with a non-hash argument" do
+      it "returns current settings if argument is nil" do
+        GC.config(nil).should == GC.config
+      end
+
+      it "raises ArgumentError for all other arguments" do
+        -> { GC.config([]) }.should.raise(ArgumentError)
+        -> { GC.config("default") }.should.raise(ArgumentError)
+        -> { GC.config(1) }.should.raise(ArgumentError)
+      end
+    end
+
+    guard -> { PlatformGuard.standard? && GC.config[:implementation] == "default" } do
+      context "with default GC implementation on MRI" do
+        before do
+          @default_config = GC.config({})
+        end
+
+        after do
+          GC.config(@default_config.except(:implementation))
+        end
+
+        it "includes :rgengc_allow_full_mark option, true by default" do
+          GC.config.should.include?(:rgengc_allow_full_mark)
+          GC.config[:rgengc_allow_full_mark].should == true
+        end
+
+        it "allows to set :rgengc_allow_full_mark" do
+          # This key maps truthy and falsey values to true and false.
+          GC.config(rgengc_allow_full_mark: nil).should == @default_config.merge(rgengc_allow_full_mark: false)
+          GC.config(rgengc_allow_full_mark: 1.23).should == @default_config.merge(rgengc_allow_full_mark: true)
+        end
+      end
+    end
+  end
+end