test: don't try to use Xcode SDK for build requirement

Library/Homebrew/extend/os/linux/extend/ENV/std.rb

@@ -2,8 +2,8 @@
 # frozen_string_literal: true
 
 module Stdenv
-  def setup_build_environment(**options)
-    generic_setup_build_environment(**options)
+  def setup_build_environment(formula: nil, cc: nil, build_bottle: false, bottle_arch: nil, testing_formula: false)
+    generic_setup_build_environment(formula: formula, cc: cc, build_bottle: build_bottle, bottle_arch: bottle_arch)
 
     prepend_path "CPATH", HOMEBREW_PREFIX/"include"
     prepend_path "LIBRARY_PATH", HOMEBREW_PREFIX/"lib"

Library/Homebrew/extend/os/linux/extend/ENV/super.rb

@@ -10,8 +10,8 @@ def self.bin
   end
 
   # @private
-  def setup_build_environment(**options)
-    generic_setup_build_environment(**options)
+  def setup_build_environment(formula: nil, cc: nil, build_bottle: false, bottle_arch: nil, testing_formula: false)
+    generic_setup_build_environment(formula: formula, cc: cc, build_bottle: build_bottle, bottle_arch: bottle_arch)
     self["HOMEBREW_OPTIMIZATION_LEVEL"] = "O2"
     self["HOMEBREW_DYNAMIC_LINKER"] = determine_dynamic_linker_path
     self["HOMEBREW_RPATH_PATHS"] = determine_rpath_paths(@formula)

Library/Homebrew/extend/os/mac/extend/ENV/std.rb

@@ -10,16 +10,16 @@ def homebrew_extra_pkg_config_paths
     ["#{HOMEBREW_LIBRARY}/Homebrew/os/mac/pkgconfig/#{MacOS.sdk_version}"]
   end
 
-  def setup_build_environment(**options)
-    generic_setup_build_environment(**options)
+  def setup_build_environment(formula: nil, cc: nil, build_bottle: false, bottle_arch: nil, testing_formula: false)
+    generic_setup_build_environment(formula: formula, cc: cc, build_bottle: build_bottle, bottle_arch: bottle_arch)
 
     # sed is strict, and errors out when it encounters files with
     # mixed character sets
     delete("LC_ALL")
     self["LC_CTYPE"] = "C"
 
     # Add lib and include etc. from the current macosxsdk to compiler flags:
-    macosxsdk(formula: @formula)
+    macosxsdk(formula: @formula, testing_formula: testing_formula)
 
     return unless MacOS::Xcode.without_clt?
 
@@ -50,15 +50,19 @@ def remove_macosxsdk(version = nil)
     remove "CMAKE_FRAMEWORK_PATH", "#{sdk}/System/Library/Frameworks"
   end
 
-  def macosxsdk(version = nil, formula: nil)
+  def macosxsdk(version = nil, formula: nil, testing_formula: false)
     # Sets all needed lib and include dirs to CFLAGS, CPPFLAGS, LDFLAGS.
     remove_macosxsdk
     min_version = version || MacOS.version
     append_to_cflags("-mmacosx-version-min=#{min_version}")
     self["CPATH"] = "#{HOMEBREW_PREFIX}/include"
     prepend "LDFLAGS", "-L#{HOMEBREW_PREFIX}/lib"
 
-    sdk = formula ? MacOS.sdk_for_formula(formula, version) : MacOS.sdk(version)
+    sdk = if formula
+      MacOS.sdk_for_formula(formula, version, check_only_runtime_requirements: testing_formula)
+    else
+      MacOS.sdk(version)
+    end
     return if !MacOS.sdk_root_needed? && sdk&.source != :xcode
 
     Homebrew::Diagnostic.checks(:fatal_setup_build_environment_checks)

Library/Homebrew/extend/os/mac/extend/ENV/super.rb

@@ -106,8 +106,7 @@ def determine_cccfg
   end
 
   # @private
-  def setup_build_environment(**options)
-    formula = options[:formula]
+  def setup_build_environment(formula: nil, cc: nil, build_bottle: false, bottle_arch: nil, testing_formula: false)
     sdk = formula ? MacOS.sdk_for_formula(formula) : MacOS.sdk
     if MacOS.sdk_root_needed? || sdk&.source == :xcode
       Homebrew::Diagnostic.checks(:fatal_setup_build_environment_checks)
@@ -122,7 +121,7 @@ def setup_build_environment(**options)
       self["HOMEBREW_SDKROOT"] = nil
       self["HOMEBREW_DEVELOPER_DIR"] = nil
     end
-    generic_setup_build_environment(**options)
+    generic_setup_build_environment(formula: formula, cc: cc, build_bottle: build_bottle, bottle_arch: bottle_arch)
 
     # Filter out symbols known not to be defined since GNU Autotools can't
     # reliably figure this out with Xcode 8 and above.

Library/Homebrew/os/mac.rb

@@ -120,9 +120,16 @@ def sdk(v = nil)
       sdk_locator.sdk_if_applicable(v)
     end
 
-    def sdk_for_formula(f, v = nil)
+    def sdk_for_formula(f, v = nil, check_only_runtime_requirements: false)
       # If the formula requires Xcode, don't return the CLT SDK
-      return Xcode.sdk if f.requirements.any? { |req| req.is_a? XcodeRequirement }
+      # If check_only_runtime_requirements is true, don't necessarily return the
+      # Xcode SDK if the XcodeRequirement is only a build or test requirment.
+      return Xcode.sdk if f.requirements.any? do |req|
+        next false unless req.is_a? XcodeRequirement
+        next false if check_only_runtime_requirements && req.build? && !req.test?
+
+        true
+      end
 
       sdk(v)
     end

Library/Homebrew/test.rb

@@ -36,7 +36,7 @@
   formula.extend(Debrew::Formula) if args.debug?
 
   ENV.extend(Stdenv)
-  T.cast(ENV, Stdenv).setup_build_environment(formula: formula)
+  T.cast(ENV, Stdenv).setup_build_environment(formula: formula, testing_formula: true)
 
   # tests can also return false to indicate failure
   Timeout.timeout TEST_TIMEOUT_SECONDS do