tests: monkey-patch exec to get coverage reports

Closes Homebrew/homebrew#48923.

Signed-off-by: Baptiste Fontaine <batifon@yahoo.fr>

Library/Homebrew/test/lib/integration_mocks.rb

@@ -6,4 +6,12 @@ module Homebrew
       end
     end
   end
+
+  def exec(*args)
+    if ENV["HOMEBREW_TESTS_COVERAGE"] && ENV["HOMEBREW_INTEGRATION_TEST"]
+      # Ensure we get coverage results before replacing the current process.
+      SimpleCov.result
+    end
+    Kernel.exec(*args)
+  end
 end

Library/Homebrew/test/test_integration_cmds.rb

@@ -28,7 +28,6 @@ class IntegrationCommandTests < Homebrew::TestCase
       -W0
       -I#{HOMEBREW_LIBRARY_PATH}/test/lib
       -rconfig
-      -rintegration_mocks
     ]
     if ENV["HOMEBREW_TESTS_COVERAGE"]
       # This is needed only because we currently use a patched version of
@@ -38,6 +37,7 @@ class IntegrationCommandTests < Homebrew::TestCase
       cmd_args << "-rbundler/setup"
       cmd_args << "-rsimplecov"
     end
+    cmd_args << "-rintegration_mocks"
     cmd_args << (HOMEBREW_LIBRARY_PATH/"../brew.rb").resolved_path.to_s
     cmd_args += args
     Bundler.with_original_env do