Extract CanOnlyWriteStrings Error

lib/dry/files/error.rb

@@ -116,5 +116,23 @@ def initialize(path)
         super("not a memory file `#{path}'")
       end
     end
+
+    # Can only write strings (i.e. not arrays, or anything else)
+    #
+    # Raised by the file system adapters
+    #
+    # @since x.x.x
+    # @api public
+    class CanOnlyWriteStringsError < Error
+      # Instantiate a new error
+      #
+      # @param path [String] path name
+      #
+      # @since x.x.x
+      # @api public
+      def initialize
+        super("Can only write strings (use `String#join` or `String#to_s`?)")
+      end
+    end
   end
 end

lib/dry/files/file_system.rb

@@ -133,6 +133,8 @@ def touch(path, **kwargs)
       # @since 0.1.0
       # @api private
       def write(path, content)
+        raise CanOnlyWriteStringsError unless content.is_a?(String)
+
         mkdir_p(path)
 
         self.open(path, WRITE_MODE) do |f|

lib/dry/files/memory_file_system/node.rb

@@ -215,7 +215,8 @@ def readlines
         # @since 0.1.0
         # @api private
         def write(content)
-          raise ArgumentError, "Join your content before trying to write it" unless content.is_a?(String)
+          raise CanOnlyWriteStringsError unless content.is_a?(String)
+
           @content = StringIO.new(content)
           @mode = DEFAULT_FILE_MODE
         end

spec/unit/dry/files/file_system_spec.rb

@@ -217,6 +217,12 @@
         path.chmod(mode)
       end
     end
+
+    it "raises error when trying to write a non-string" do
+      path = root.join("write")
+      expect { subject.write(path, %w[hello world]) }
+        .to raise_error(Dry::Files::CanOnlyWriteStringsError)
+    end
   end
 
   describe "#join" do

spec/unit/dry/files/memory_file_system_spec.rb

@@ -188,6 +188,12 @@
         path.chmod(mode)
       end
     end
+
+    it "raises error when trying to write a non-string" do
+      path = subject.join("write")
+      expect { subject.write(path, %w[hello world]) }
+        .to raise_error(Dry::Files::CanOnlyWriteStringsError)
+    end
   end
 
   describe "#join" do