Add specs to verify ClosedError is raised

spec/mfile_spec.cr

@@ -0,0 +1,63 @@
+require "spec"
+require "../src/lavinmq/mfile"
+
+module MFileSpec
+  def self.with_file(&)
+    file = File.tempfile "mfile_spec"
+    yield file
+  ensure
+    file.delete unless file.nil?
+  end
+
+  describe MFile do
+    describe "#write" do
+      it "should raise ClosedError if closed" do
+        with_file do |file|
+          mfile = MFile.new file.path
+          mfile.close
+          expect_raises(MFile::ClosedError) { mfile.write "foo".to_slice }
+        end
+      end
+    end
+    describe "#read" do
+      it "should raise ClosedError if closed" do
+        with_file do |file|
+          mfile = MFile.new file.path
+          mfile.close
+          data = Bytes.new(1)
+          expect_raises(MFile::ClosedError) { mfile.read data }
+        end
+      end
+    end
+    describe "#to_slice" do
+      describe "without position and size" do
+        it "should raise ClosedError if closed" do
+          with_file do |file|
+            mfile = MFile.new file.path
+            mfile.close
+            expect_raises(MFile::ClosedError) { mfile.to_slice }
+          end
+        end
+      end
+      describe "with position and size" do
+        it "should raise ClosedError if closed" do
+          with_file do |file|
+            mfile = MFile.new file.path
+            mfile.close
+            expect_raises(MFile::ClosedError) { mfile.to_slice(1, 1) }
+          end
+        end
+      end
+    end
+    describe "#copy_to" do
+      it "should raise ClosedError if closed" do
+        with_file do |file|
+          mfile = MFile.new file.path
+          mfile.close
+          data = IO::Memory.new
+          expect_raises(MFile::ClosedError) { mfile.copy_to data }
+        end
+      end
+    end
+  end
+end

src/lavinmq/mfile.cr

@@ -142,6 +142,7 @@ class MFile < IO
   # Copies the file to another IO
   # Won't mmap the file if it's unmapped already
   def copy_to(output : IO, size = @size) : Int64
+    raise ClosedError.new if @closed
     if unmapped? # don't remap unmapped files
       io = IO::FileDescriptor.new(@fd, blocking: true, close_on_finalize: false)
       io.rewind