Deactivate previous env before activating new one (#25409)

* Deactivate previous env before activating new one

Currently on develop you can run `spack env activate` multiple times to switch
between environments, but they leave traces, even though Spack only supports
one active environment at a time.

Currently:

```console
$ spack env create a
$ spack env create b
$ spack env activate -p a
[a] $ spack env activate -p b
[b] [a] $ spack env activate -p b
[a] [b] [a] $ spack env activate -p a
[a] [b] [c] $ echo $MANPATH | tr ":" "\n"
/path/to/environments/a/.spack-env/view/share/man
/path/to/environments/a/.spack-env/view/man
/path/to/environments/b/.spack-env/view/share/man
/path/to/environments/b/.spack-env/view/man
```

This PR fixes that:

```console
$ spack env activate -p a
[a] $ spack env activate -p b
[b] $ spack env activate -p a
[a] $ echo $MANPATH | tr ":" "\n"
/path/to/environments/a/.spack-env/view/share/man
/path/to/environments/a/.spack-env/view/man
```

1 files changed, 9 insertions, 3 deletions

diff --git a/share/spack/qa/setup-env-test.sh b/share/spack/qa/setup-env-test.sh
index 88e30aefeb..bddf7ca1af 100755
--- a/share/spack/qa/setup-env-test.sh
+++ b/share/spack/qa/setup-env-test.sh
@@ -70,13 +70,13 @@ b_module=$(spack -m module tcl find b)
 # Create a test environment for testing environment commands
 echo "Creating a mock environment"
 spack env create spack_test_env
-test_env_location=$(spack location -e spack_test_env)
+spack env create spack_test_2_env
 
 # Ensure that we uninstall b on exit
 cleanup() {
     echo "Removing test environment before exiting."
     spack env deactivate 2>&1 > /dev/null
-    spack env rm -y spack_test_env
+    spack env rm -y spack_test_env spack_test_2_env
 
     title "Cleanup"
     echo "Removing test packages before exiting."
@@ -178,4 +178,10 @@ echo "Testing 'spack env activate --temp'"
 spack env activate --temp
 is_set SPACK_ENV
 spack env deactivate
-is_not_set SPACK_ENV
\ No newline at end of file
+is_not_set SPACK_ENV
+
+echo "Testing spack env activate repeatedly"
+spack env activate spack_test_env
+spack env activate spack_test_2_env
+contains "spack_test_2_env" sh -c 'echo $PATH'
+does_not_contain "spack_test_env" sh -c 'echo $PATH'