How to change DRY a spec to avoid deprecation warning "The implicit block expectation syntax is deprecated, you should pass a block..."

I have to following rspec fragment:

describe "Create with a classification class added" do
  before do
    @lambda_block = lambda {
      click_button I18n.t(:button_save)
      expect(page).to have_text(I18n.t :'flash.classification_scheme.create_success')
    }     
  end   

  describe "Save should create a ClassificationScheme and a ClassificationSchemesClass" do
    subject { @lambda_block }
    it { is_expected.to change(ClassificationScheme, :count).by(1) }
    it { is_expected.to change(ClassificationSchemesClass, :count).by(1) }
  end   
end   

I get these deprecation warnings:

The implicit block expectation syntax is deprecated, you should pass a block rather than an argument to expect to use the provided block expectation matcher or the matcher must implement supports_value_expectations?. e.g expect { value }.to change ClassificationScheme.count by 1 not expect(value).to change ClassificationScheme.count by 1

The implicit block expectation syntax is deprecated, you should pass a block rather than an argument to expect to use the provided block expectation matcher or the matcher must implement supports_value_expectations?. e.g expect { value }.to change ClassificationSchemesClass.count by 1 not expect(value).to change ClassificationSchemesClass.count by 1

The deprecation warnings disappear if I change the spec as follows. expect gets a block instead of an argument, however two lines are repeated, the code is not DRY.

describe "Create with a classification class added" do 
  it "Save should create a ClassificationScheme" do
    expect{
      click_button I18n.t(:button_save)
      expect(page).to have_text(I18n.t :'flash.classification_scheme.create_success')
    }.to change{ClassificationScheme.count}.by(1)
  end

  it "Save should create a ClassificationSchemesClass" do
    expect{
      click_button I18n.t(:button_save)
      expect(page).to have_text(I18n.t :'flash.classification_scheme.create_success')
    }.to change{ClassificationSchemesClass.count}.by(1)
  end
end

How can I pass the lambda block to expect?

If I try expect{@lambda_block}.to change... then the lambda block is not executed. If I try expect(@lambda_block).to change... then the test is passed, however I get again the deprecation warning.

The question is, how can I pass the @lambda_block to expect but avoid the deprecation warning.

I'm currently to migrate a project from rails 5 to rails 6, so the current versions:
rails 6.0.6.1
rspec 3.12.0
rspec-rails 5.1.2

Just to make it nice and clear to see what you have, I've simplified this a bit:

subject do
  lambda { click_button I18n.t(:button_save) }     
end
it { is_expected.to change(ClassificationScheme, :count).by(1) }

When you change to explicit block, you no longer need lambda:

subject do
  click_button I18n.t(:button_save)    
end
it { expect { subject }.to change(ClassificationScheme, :count).by(1) }
#           ^         ^
# the block is already being passed to expect, this is where your lambda used to be

When you put lambda inside of that block, the blocks become nested and lambda never gets called. Which you can also fix by calling it yourself:

subject do
  lambda { click_button I18n.t(:button_save) }     
end
it { expect { subject.call }.to change(ClassificationScheme, :count).by(1) }

When you don't use a block syntax { } or do end, subject becomes an argument, which is deprecated:

#               block has to go here vvvvvv
def expect(arg = nil, keyword: :arg, &block)
# not here ^^^  
end

You can use ruby unary & operator to treat passed argument as a block:

subject do
  lambda { click_button I18n.t(:button_save) }     
end
it { expect(&subject).to change(ClassificationScheme, :count).by(1) }

This one is hard to explain quick:
https://medium.com/@amliving/rubys-unary-operator-a93d36d3cd8b