Try something naive

.cirrus.yml

@@ -3,5 +3,15 @@ task:
   freebsd_instance:
     image_family: freebsd-14-0
   install_script: pkg install -y ghc hs-cabal-install git autoconf bash
+  setup_script:
+    - ./.cirrus/ci.sh setup_freebsd
+    - ./.cirrus/ci.sh configure_freebsd
+  haskell_cache:
+    folder: ~/.cabal/store
+    fingerprint_script:
+      - export PLAN_HASH=$(sha256sum ./dist-newstyle/cache/plan.json | awk '{print $1}')
+      - echo "ghc-9.8.2-$PLAN_HASH"
+
   script:
-    - ./.cirrus/ci.sh build_freebd
+    - ./.cirrus/ci.sh build_freebsd
+    - ./.cirrus/ci.sh test_freebsd

.cirrus/ci.sh

@@ -2,22 +2,37 @@
 
 set -xEeuo pipefail
 
-build_freebsd() {
+setup_freebsd() {
   export GHCUP_INSTALL_BASE_PREFIX="/opt/ghc/"
   mkdir -p ~/.local/ghcup/bin/
+  mkdir -p /opt/ghcup/bin/
   curl -L https://downloads.haskell.org/~ghcup/x86_64-portbld-freebsd-ghcup --output /opt/ghcup/bin/ghcup
   chmod +x /opt/ghcup/bin/ghcup
   ghcup install ghc 9.8.2
   ghcup set ghc 9.8.2
   ghcup install cabal 3.12.1.0
+  cabal update
+}
+
+configure_freebsd() {
+  cabal freeze --project-file=cabal.release.project
+}
+
+build_freebsd() {
+  cabal build --project-file=cabal.release.project all -j
+}
+
+test_freebsd() {
+  cabal test --project-file=cabal.release.project all -j
 }
 
 help() {
-  echo "Run with \`build_freebsd\`"
+  echo "Run with setup_freebsd, configure_freebsd, build_freebsd or test_freebsd."
 }
 
 case ${1:-help} in
   help) help ;;
-  build_frebsd) build_freebsd ;;
-
+  setup_freebsd) setup_freebsd ;;
+  build_freebsd) build_freebsd ;;
+  test_freebsd) test_freebsd ;;
 esac