fix test isolation

Make sur that PYENV_TEST_DIR is created if mktemp failed
mock python3 usage by updating create_executable function
fix test by adding the right PATH
update path in plugin test
replace for loop with while read
don't use symlink for stub

test/exec.bats

@@ -8,7 +8,7 @@ create_executable() {
   bin="${PYENV_ROOT}/versions/${PYENV_VERSION}/bin"
   mkdir -p "$bin"
   { if [ $# -eq 0 ]; then cat -
-    else echo "$@"
+    else printf '%s\n' "$@"
     fi
   } | sed -Ee '1s/^ +//' > "${bin}/$name"
   chmod +x "${bin}/$name"
@@ -85,18 +85,25 @@ OUT
 }
 
 @test "sys.executable with system version (#98)" {
-  system_python="$(python3 -c 'import sys; print(sys.executable)')"
+  export PATH="${PYENV_ROOT}/versions/bin:${PATH}"
+  create_executable "python3" <<SH
+#!$BASH
+echo system
+SH
+  system_python="$(python3)"
+  assert_equal "${system_python}" "system"
 
-  PYENV_VERSION="custom"
-  create_executable "python3" ""
-  unset PYENV_VERSION
+  export PYENV_VERSION="custom"
+  create_executable "python3" "#!/bin/sh" "echo custom"
 
   pyenv-rehash
-  run pyenv-exec python3 -c 'import sys; print(sys.executable)'
-  assert_success "${system_python}"
+
+  custom_python="$(pyenv-exec python3)"
+  assert_equal "${custom_python}" "custom"
 }
 
 @test 'PATH is not modified with system Python' {
+  export PATH="${PYENV_TEST_DIR}:${PATH}"
   # Create a wrapper executable that verifies PATH.
   PYENV_VERSION="custom"
   create_executable "python3" '[[ "$PATH" == "${PYENV_TEST_DIR}/root/versions/custom/bin:"* ]] || { echo "unexpected:$PATH"; exit 2;}'
@@ -104,7 +111,13 @@ OUT
   pyenv-rehash
 
   # Path is not modified with system Python.
-  run pyenv-exec python3 -c 'import os; print(os.getenv("PATH"))'
+  cat > "${PYENV_TEST_DIR}/python3" <<SH
+#!$BASH
+echo \$PATH
+SH
+  chmod +x "${PYENV_TEST_DIR}/python3"
+  pyenv-rehash
+  run pyenv-exec python3
   assert_success "$PATH"
 
   # Path is modified with custom Python.
@@ -116,6 +129,6 @@ OUT
   assert_success
 
   # Path is not modified with system:custom Python.
-  PYENV_VERSION=system:custom run pyenv-exec python3 -c 'import os; print(os.getenv("PATH"))'
+  PYENV_VERSION=system:custom run pyenv-exec python3
   assert_success "$PATH"
 }

test/prefix.bats

@@ -20,7 +20,7 @@ load test_helper
   mkdir -p "${PYENV_TEST_DIR}/bin"
   touch "${PYENV_TEST_DIR}/bin/python"
   chmod +x "${PYENV_TEST_DIR}/bin/python"
-  PYENV_VERSION="system" run pyenv-prefix
+  PATH="${PYENV_TEST_DIR}/libexec:$PATH" PYENV_VERSION="system" run pyenv-prefix
   assert_success "$PYENV_TEST_DIR"
 }
 
@@ -40,7 +40,7 @@ load test_helper
 echo /bin/python
 OUT
   chmod +x "${BATS_TEST_DIRNAME}/libexec/pyenv-which"
-  PYENV_VERSION="system" run pyenv-prefix
+  PATH="${PYENV_TEST_DIR}/libexec:$PATH" PYENV_VERSION="system" run pyenv-prefix
   assert_success "/"
   rm -f "${BATS_TEST_DIRNAME}/libexec/pyenv-which"
 }

test/test_helper.bash

@@ -5,6 +5,7 @@ unset PYENV_DIR
 if [ -z "$PYENV_TEST_DIR" ]; then
   PYENV_TEST_DIR="${BATS_TMPDIR}/pyenv"
   export PYENV_TEST_DIR="$(mktemp -d "${PYENV_TEST_DIR}.XXX" 2>/dev/null || echo "$PYENV_TEST_DIR")"
+  mkdir -p "${PYENV_TEST_DIR}"
 
   if enable -f "${BATS_TEST_DIRNAME}"/../libexec/pyenv-realpath.dylib realpath 2>/dev/null; then
     export PYENV_TEST_DIR="$(realpath "$PYENV_TEST_DIR")"

test/versions.bats

@@ -238,6 +238,7 @@ OUT
 }
 
 @test "non-bare output shows symlink contents" {
+  stub_system_python
   create_version "1.9.0"
   create_alias "link" "1.9.0"