Remove `Sha256Helper`.

Library/Homebrew/cask/spec/cask/audit_spec.rb

 describe Hbc::Audit do
   include AuditMatchers
-  include Sha256Helper
 
   let(:cask) { instance_double(Hbc::Cask) }
   let(:download) { false }
@@ -178,7 +177,7 @@ describe Hbc::Audit do
           end
 
           context "when appcast checkpoint is out of date" do
-            let(:actual_checkpoint) { random_sha256 }
+            let(:actual_checkpoint) { "deadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeef" }
             it { is_expected.to warn_with(mismatch_msg) }
             it { should_not warn_with(curl_error_msg) }
           end

Library/Homebrew/cask/spec/cask/verify/checksum_spec.rb

 describe Hbc::Verify::Checksum do
-  include Sha256Helper
-
   let(:cask) { double("cask") }
   let(:downloaded_path) { double("downloaded_path") }
   let(:verification) { described_class.new(cask, downloaded_path) }
@@ -35,7 +33,7 @@ describe Hbc::Verify::Checksum do
     end
 
     context "sha256 is a valid shasum" do
-      let(:sha256) { random_sha256 }
+      let(:sha256) { "deadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeef" }
 
       it { is_expected.to be true }
     end
@@ -44,7 +42,7 @@ describe Hbc::Verify::Checksum do
   describe "#verify" do
     subject { verification.verify }
 
-    let(:computed) { random_sha256 }
+    let(:computed) { "deadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeef" }
 
     before do
       allow(verification).to receive(:computed).and_return(computed)
@@ -67,7 +65,7 @@ describe Hbc::Verify::Checksum do
     end
 
     context "sha256 does not match computed" do
-      let(:sha256) { random_sha256 }
+      let(:sha256) { "d3adb33fd3adb33fd3adb33fd3adb33fd3adb33fd3adb33fd3adb33fd3adb33f" }
 
       it "raises an error" do
         expect { subject }.to raise_error(Hbc::CaskSha256MismatchError)

Library/Homebrew/cask/spec/support/sha256_helper.rb

-require"digest"
-
-module Sha256Helper
-  def random_sha256
-    seed = "--#{rand(10_000)}--#{Time.now}--"
-    Digest::SHA2.hexdigest(seed)
-  end
-end