add more docs tests.

test/docs/mechanics_test.rb

@@ -78,9 +78,65 @@ def validate(ctx, params:, **)
 
     result = Memo::Operation::Create.call(params: {memo: nil})
     assert_equal result.success?, true
+
+    user = Object
+    assert_raises ArgumentError do
+      #:kwargs-error
+      result = Memo::Operation::Create.call(current_user: user)
+      #=> ArgumentError: missing keyword: :params
+      #       memo/operation/create.rb:9:in `validate'
+      #:kwargs-error end
+    end
   end
 end
 
+class WriteToCtx_DocsMechanicsTest < Minitest::Spec
+  Memo = Class.new do
+    def initialize(*); end
+  end
+  it "what" do
+    #:ctx-write-read
+    module Memo::Operation
+      class Create < Trailblazer::Operation
+        step :validate
+        step :save # sets ctx[:model]
+        step :notify
+        #~body
+        #~meths
+        def validate(ctx, params:, **)
+          true
+        end
+
+        def send_email(*)
+          true
+        end
+        #~meths end
+        #:ctx-write
+        def save(ctx, params:, **)
+          ctx[:model] = Memo.new(params[:memo])
+        end
+        #~body end
+        #:ctx-write end
+        def notify(ctx, model:, **)
+          send_email(model)
+        end
+      end
+    end
+    #:ctx-write-read end
+
+    result = Memo::Operation::Create.call(params: {memo: nil})
+    assert_equal result.success?, true
+
+    user = Object
+    assert_raises ArgumentError do
+      #:kwargs-error
+      result = Memo::Operation::Create.call(current_user: user)
+      #=> ArgumentError: missing keyword: :params
+      #       memo/operation/create.rb:9:in `validate'
+      #:kwargs-error end
+    end
+  end
+end
 
 class Classmethod_DocsMechanicsTest < Minitest::Spec
   Memo = Module.new