Use curl stub instead of aria2c during tests (equiv to rbenv/ruby-build#965)

plugins/python-build/test/test_helper.bash

@@ -9,6 +9,39 @@ if [ "$FIXTURE_ROOT" != "$BATS_TEST_DIRNAME/fixtures" ]; then
   export PATH
 fi
 
+remove_command_from_path() {
+  OLDIFS="${IFS}"
+  local cmd="$1"
+  local path
+  local paths=()
+  IFS=:
+  for path in ${PATH}; do
+    if [ -e "${path}/${cmd}" ]; then
+      local tmp_path="$(mktemp -d "${TMP}/path.XXXXX")"
+      ln -fs "${path}"/* "${tmp_path}"
+      rm -f "${tmp_path}/${cmd}"
+      paths["${#paths[@]}"]="${tmp_path}"
+    else
+      paths["${#paths[@]}"]="${path}"
+    fi
+  done
+  export PATH="${paths[*]}"
+  IFS="${OLDIFS}"
+}
+
+ensure_not_found_in_path() {
+  local cmd
+  for cmd; do
+    if command -v "${cmd}" 1>/dev/null 2>&1; then
+      remove_command_from_path "${cmd}"
+    fi
+  done
+}
+
+setup() {
+  ensure_not_found_in_path aria2c
+}
+
 teardown() {
   rm -fr "${TMP:?}"/*
 }