[rubygems/rubygems] Improve bundle exec with default gems specs

Make them more consistent and not silently pass even if something
regresses. These specs had a typo that made the assertion be that the
`erb --version` output includes the empty string which is always
obviously true.

ruby/rubygems@451e07c305

Author: deivid-rodriguez

spec/bundler/commands/exec_spec.rb

@@ -193,17 +193,20 @@
   end
 
   context "with default gems" do
-    let(:default_erb_version) { ruby "gem 'erb', '< 999999'; require 'erb/version'; puts Erb::VERSION", raise_on_error: false }
+    # TODO: Switch to ERB::VERSION once Ruby 3.4 support is dropped, so all
+    # supported rubies include an `erb` gem version where `ERB::VERSION` is
+    # public
+    let(:default_erb_version) { ruby "require 'erb/version'; puts ERB.const_get(:VERSION)" }
 
     context "when not specified in Gemfile" do
       before do
         install_gemfile "source \"https://gem.repo1\""
       end
 
       it "uses version provided by ruby" do
-        bundle "exec erb --version"
+        bundle "exec erb --version", artifice: nil
 
-        expect(out).to include(default_erb_version)
+        expect(stdboth).to eq(default_erb_version)
       end
     end
 
@@ -226,8 +229,7 @@
       it "uses version specified" do
         bundle "exec erb --version", artifice: nil
 
-        expect(out).to eq(specified_erb_version)
-        expect(err).to be_empty
+        expect(stdboth).to eq(specified_erb_version)
       end
     end
 
@@ -249,13 +251,12 @@
           source "https://gem.repo2"
           gem "gem_depending_on_old_erb"
         G
-
-        bundle "exec erb --version", artifice: nil
       end
 
       it "uses resolved version" do
-        expect(out).to eq(indirect_erb_version)
-        expect(err).to be_empty
+        bundle "exec erb --version", artifice: nil
+
+        expect(stdboth).to eq(indirect_erb_version)
       end
     end
   end