Manually fix RuboCop RSpec autofix failures.

Library/Homebrew/test/cache_store_spec.rb

@@ -126,7 +126,7 @@ describe CacheStoreDatabase do
 
     context "`File.exist?(cache_path)` returns `true`" do
       before do
-        allow(File).to receive(:exist?).with(cache_path).and_return(true)
+        allow(cache_path).to receive(:exist?).and_return(true)
       end
 
       it "returns `true`" do
@@ -136,7 +136,7 @@ describe CacheStoreDatabase do
 
     context "`File.exist?(cache_path)` returns `false`" do
       before do
-        allow(File).to receive(:exist?).with(cache_path).and_return(false)
+        allow(cache_path).to receive(:exist?).and_return(false)
       end
 
       it "returns `false`" do

Library/Homebrew/test/error_during_execution_spec.rb

@@ -44,7 +44,7 @@ describe ErrorDuringExecution do
       end
 
       its(:to_s) {
-        expect(subject).to eq <<~EOS
+        expect(subject.to_s).to eq <<~EOS
           Failure while executing; `false` exited with 1. Here's the output:
           This still worked.
           #{Formatter.error("Here something went wrong.\n")}
@@ -56,8 +56,8 @@ describe ErrorDuringExecution do
       let(:command) { ["env", "PATH=/bin", "cat", "with spaces"] }
 
       its(:to_s) {
-        expect(subject)
-        .to eq 'Failure while executing; `env PATH=/bin cat with\ spaces` exited with 1.'
+        expect(subject.to_s)
+          .to eq 'Failure while executing; `env PATH=/bin cat with\ spaces` exited with 1.'
       }
     end
   end

Library/Homebrew/test/exceptions_spec.rb

@@ -16,7 +16,7 @@ describe FormulaValidationError do
   subject { described_class.new("foo", "sha257", "magic") }
 
   its(:to_s) {
-    expect(subject).to eq(%q(invalid attribute for formula 'foo': sha257 ("magic")))
+    expect(subject.to_s).to eq(%q(invalid attribute for formula 'foo': sha257 ("magic")))
   }
 end
 
@@ -49,7 +49,7 @@ describe FormulaUnavailableError do
     end
 
     its(:to_s) {
-      expect(subject).to eq('No available formula with the name "foo" (dependency of foobar)')
+      expect(subject.to_s).to eq('No available formula with the name "foo" (dependency of foobar)')
     }
   end
 end
@@ -76,7 +76,7 @@ describe FormulaClassUnavailableError do
     let(:list) { [] }
 
     its(:to_s) {
-      expect(subject).to match(/Expected to find class Foo, but found no classes\./)
+      expect(subject.to_s).to match(/Expected to find class Foo, but found no classes\./)
     }
   end
 
@@ -84,7 +84,7 @@ describe FormulaClassUnavailableError do
     let(:list) { [mod.const_get(:Bar)] }
 
     its(:to_s) {
-      expect(subject).to match(/Expected to find class Foo, but only found: Bar \(not derived from Formula!\)\./)
+      expect(subject.to_s).to match(/Expected to find class Foo, but only found: Bar \(not derived from Formula!\)\./)
     }
   end