Reduce boilerplate in tests

test/build.bats

@@ -128,24 +128,18 @@ OUT
 }
 
 @test "mruby strategy overwrites non-writable files" {
-  mkdir -p "$RUBY_BUILD_CACHE_PATH"
-  cd "$RUBY_BUILD_CACHE_PATH"
-  mkdir -p "mruby-1.0/build/host/bin"
-  touch "mruby-1.0/build/host/bin"/{mruby,mirb}
-  tar czf "mruby-1.0.tar.gz" "mruby-1.0"
+  cached_tarball "mruby-1.0" build/host/bin/{mruby,mirb}
 
   mkdir -p "$INSTALL_ROOT/bin"
   touch "$INSTALL_ROOT/bin/mruby"
   chmod -w "$INSTALL_ROOT/bin/mruby"
 
-  cat > "definition" <<DEF
-install_package "mruby-1.0" "http://ruby-lang.org/pub/mruby-1.0.tar.gz" mruby
-DEF
-
   stub gem false
   stub rake '--version : true' true
 
-  run ruby-build "definition" "$INSTALL_ROOT"
+  run_inline_definition <<DEF
+install_package "mruby-1.0" "http://ruby-lang.org/pub/mruby-1.0.tar.gz" mruby
+DEF
   assert_success
 
   unstub rake
@@ -158,11 +152,6 @@ DEF
 @test "rbx uses bundle then rake" {
   cached_tarball "rubinius-2.0.0" "Gemfile"
 
-  cd "$TMP"
-  cat > "definition" <<DEF
-install_package "rubinius-2.0.0" "http://releases.rubini.us/rubinius-2.0.0.tar.gz" rbx
-DEF
-
   stub gem false
   stub rake false
   stub bundle \
@@ -171,7 +160,9 @@ DEF
     '--version : true' \
     " exec rake install : { cat build.log; echo bundle \"\$@\"; } >> '$INSTALL_ROOT/build.log'"
 
-  run ruby-build "definition" "$INSTALL_ROOT"
+  run_inline_definition <<DEF
+install_package "rubinius-2.0.0" "http://releases.rubini.us/rubinius-2.0.0.tar.gz" rbx
+DEF
   assert_success
 
   unstub bundle

test/test_helper.bash

@@ -44,6 +44,12 @@ unstub() {
   return "$STATUS"
 }
 
+run_inline_definition() {
+  local definition="${TMP}/build-definition"
+  cat > "$definition"
+  run ruby-build "$definition" "${1:-$INSTALL_ROOT}"
+}
+
 install_fixture() {
   local name="$1"
   local destination="$2"