diff --git a/.github/workflows/test-per-system.yml b/.github/workflows/test-per-system.yml
new file mode 100644
index 0000000..2c5cd87
--- /dev/null
+++ b/.github/workflows/test-per-system.yml
@@ -0,0 +1,97 @@
+name: Test Runner
+
+on:
+  workflow_call:
+    inputs:
+      runs-on:
+        description: 'GitHub Actions runner to use (e.g., ubuntu-latest, macos-13)'
+        required: true
+        type: string
+      system:
+        description: 'Target system architecture (e.g., x86_64-linux, aarch64-darwin)'
+        required: true
+        type: string
+      oldest_installer_version:
+        description: 'Oldest supported Nix installer version to test (e.g., nix-2.8.0)'
+        required: true
+        type: string
+
+env:
+  nixpkgs_channel: nixpkgs=channel:nixos-25.05
+
+jobs:
+  simple-build:
+    runs-on: ${{ inputs.runs-on }}
+    steps:
+    - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+    - name: Install Nix
+      uses: ./
+      with:
+        nix_path: ${{ env.nixpkgs_channel }}
+    - name: Test environment variables
+      run: ./tests/test-env.sh
+    - run: nix-env -iA cachix -f https://cachix.org/api/v1/install
+    - run: cat /etc/nix/nix.conf
+    # cachix should be available and be able to configure a cache
+    - run: cachix use cachix
+    - run: nix-build tests/test-build.nix
+
+  custom-nix-path:
+    runs-on: ${{ inputs.runs-on }}
+    steps:
+    - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+    - name: Install Nix
+      uses: ./
+      with:
+        nix_path: ${{ env.nixpkgs_channel }}
+    - run: test $NIX_PATH == '${{ env.nixpkgs_channel }}'
+    - run: nix-build tests/test-build.nix
+
+  extra-nix-config:
+    runs-on: ${{ inputs.runs-on }}
+    steps:
+    - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+    - name: Install Nix
+      uses: ./
+      with:
+        nix_path: ${{ env.nixpkgs_channel }}
+        extra_nix_config: |
+          sandbox = relaxed
+    - run: cat /etc/nix/nix.conf
+    - run: nix-build tests/test-build.nix --arg noChroot true
+
+  flakes:
+    runs-on: ${{ inputs.runs-on }}
+    steps:
+    - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+    - name: Install Nix
+      uses: ./
+    - run: nix flake show github:NixOS/nixpkgs
+
+  latest-installer:
+    runs-on: ${{ inputs.runs-on }}
+    steps:
+    - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+    - name: Run NAR server
+      run: |
+        curl --location https://github.com/cachix/nar-toolbox/releases/download/v0.1.0/nar-toolbox-${{ inputs.system }} -O
+        chmod +x ./nar-toolbox-${{ inputs.system }}
+        ./nar-toolbox-${{ inputs.system }} serve https://cache.nixos.org &
+    - name: Install Nix
+      uses: ./
+      with:
+        nix_path: ${{ env.nixpkgs_channel }}
+        install_url: https://hydra.nixos.org/job/nix/master/installerScript/latest-finished/download/1/install
+        install_options: "--tarball-url-prefix http://localhost:8080"
+    - run: nix-build tests/test-build.nix
+
+  oldest-supported-installer:
+    runs-on: ${{ inputs.runs-on }}
+    steps:
+    - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+    - name: Install Nix
+      uses: ./
+      with:
+        nix_path: ${{ env.nixpkgs_channel }}
+        install_url: https://releases.nixos.org/nix/${{ inputs.oldest_installer_version }}/install
+    - run: nix-build tests/test-build.nix
\ No newline at end of file
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 7b3884b..6542c67 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -10,143 +10,43 @@ env:
   nixpkgs_channel: nixpkgs=channel:nixos-25.05
 
 jobs:
-  simple-build:
-    strategy:
-      fail-fast: false
-      matrix:
-        os:
-        - ubuntu-latest
-        - ubuntu-24.04-arm
-        - macos-latest
-        - macos-13
-    runs-on: ${{ matrix.os }}
-    steps:
-    - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
-    - name: Install Nix
-      uses: ./
-      with:
-        nix_path: ${{ env.nixpkgs_channel }}
-    - run: nix-env -iA cachix -f https://cachix.org/api/v1/install
-    - run: cat /etc/nix/nix.conf
-    # cachix should be available and be able to configure a cache
-    - run: cachix use cachix
-    - run: nix-build test.nix
-
-  custom-nix-path:
-    strategy:
-      fail-fast: false
-      matrix:
-        os:
-        - ubuntu-latest
-        - ubuntu-24.04-arm
-        - macos-latest
-        - macos-13
-    runs-on: ${{ matrix.os }}
-    steps:
-    - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
-    - name: Install Nix
-      uses: ./
-      with:
-        nix_path: ${{ env.nixpkgs_channel }}
-    - run: test $NIX_PATH == '${{ env.nixpkgs_channel }}'
-    - run: nix-build test.nix
-
-  extra-nix-config:
-    strategy:
-      fail-fast: false
-      matrix:
-        os:
-        - ubuntu-latest
-        - ubuntu-24.04-arm
-        - macos-latest
-        - macos-13
-    runs-on: ${{ matrix.os }}
-    steps:
-    - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
-    - name: Install Nix
-      uses: ./
-      with:
-        nix_path: ${{ env.nixpkgs_channel }}
-        extra_nix_config: |
-          sandbox = relaxed
-    - run: cat /etc/nix/nix.conf
-    - run: nix-build test.nix --arg noChroot true
-
-  flakes:
-    strategy:
-      fail-fast: false
-      matrix:
-        os:
-        - ubuntu-latest
-        - ubuntu-24.04-arm
-        - macos-latest
-        - macos-13
-    runs-on: ${{ matrix.os }}
-    steps:
-    - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
-    - name: Install Nix
-      uses: ./
-    - run: nix flake show github:NixOS/nixpkgs
-
-  latest-installer:
+  test:
     strategy:
       fail-fast: false
       matrix:
         include:
-          - os: ubuntu-latest
+          - runs-on: ubuntu-latest
             system: x86_64-linux
-          - os: ubuntu-24.04-arm
+            oldest_installer_version: nix-2.8.0
+          - runs-on: ubuntu-24.04-arm
             system: aarch64-linux
-          - os: macos-latest
+            oldest_installer_version: nix-2.8.0
+          - runs-on: ubuntu-22.04
+            system: x86_64-linux
+            oldest_installer_version: nix-2.8.0
+          - runs-on: macos-latest
             system: aarch64-darwin
-          - os: macos-13
+            oldest_installer_version: nix-2.18.6
+          - runs-on: macos-26
+            system: aarch64-darwin
+            oldest_installer_version: nix-2.18.6
+          - runs-on: macos-15
+            system: aarch64-darwin
+            oldest_installer_version: nix-2.18.6
+          - runs-on: macos-14
+            system: aarch64-darwin
+            oldest_installer_version: nix-2.8.0
+          - runs-on: macos-13
             system: x86_64-darwin
-    runs-on: ${{ matrix.os }}
-    steps:
-    - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
-    - name: Run NAR server
-      run: |
-        curl --location https://github.com/cachix/nar-toolbox/releases/download/v0.1.0/nar-toolbox-${{ matrix.system }} -O
-        chmod +x ./nar-toolbox-${{ matrix.system }}
-        ./nar-toolbox-${{ matrix.system }} serve https://cache.nixos.org &
-    - name: Install Nix
-      uses: ./
-      with:
-        nix_path: ${{ env.nixpkgs_channel }}
-        install_url: https://hydra.nixos.org/job/nix/master/installerScript/latest-finished/download/1/install
-        install_options: "--tarball-url-prefix http://localhost:8080"
-    - run: nix-build test.nix
-
-  oldest-supported-installer:
-    strategy:
-      fail-fast: false
-      matrix:
-        include:
-          - os: ubuntu-latest
-            installer_version: nix-2.8.0
-          - os: ubuntu-24.04-arm
-            installer_version: nix-2.8.0
-          - os: macos-latest
-            # macOS 15 Sequoia took over some of the ids previously used for _nixbld
-            # 2.18.6 is the oldest version that was patched for this.
-            installer_version: nix-2.18.6
-          - os: macos-13
-            installer_version: nix-2.8.0
-    runs-on: ${{ matrix.os }}
-    steps:
-    - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
-    - name: Install Nix
-      uses: ./
-      with:
-        nix_path: ${{ env.nixpkgs_channel }}
-        install_url: https://releases.nixos.org/nix/${{ matrix.installer_version }}/install
-    - run: nix-build test.nix
+            oldest_installer_version: nix-2.8.0
+    uses: ./.github/workflows/test-per-system.yml
+    with:
+      runs-on: ${{ matrix.runs-on }}
+      system: ${{ matrix.system }}
+      oldest_installer_version: ${{ matrix.oldest_installer_version }}
 
   act-support:
-    strategy:
-      matrix:
-        os: [ubuntu-latest]
-    runs-on: ${{ matrix.os }}
+    runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
     - run: curl https://raw.githubusercontent.com/nektos/act/master/install.sh | sudo bash
diff --git a/install-nix.sh b/install-nix.sh
index 61356ac..abf5c18 100755
--- a/install-nix.sh
+++ b/install-nix.sh
@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
-if nix_path="$(type -p nix)" ; then
+if nix_path="$(type -p nix)"; then
   echo "Aborting: Nix is already installed at ${nix_path}"
   exit
 fi
@@ -26,11 +26,13 @@ trap 'rm -rf "$workdir"' EXIT
 
 # Configure Nix
 add_config() {
-  echo "$1" >> "$workdir/nix.conf"
+  echo "$1" >>"$workdir/nix.conf"
 }
 add_config "show-trace = true"
 # Set jobs to number of cores
 add_config "max-jobs = auto"
+# Configure the nix-daemon to use certificates.
+# In multi-user installs, NIX_SSL_CERT_FILE only works if set in the daemon's service file.
 if [[ $OSTYPE =~ darwin ]]; then
   add_config "ssl-cert-file = /etc/ssl/cert.pem"
 fi
@@ -70,8 +72,14 @@ installer_options=(
   --nix-extra-conf-file "$workdir/nix.conf"
 )
 
-# only use the nix-daemon settings if on darwin (which get ignored) or systemd is supported
+# Enable daemon on macOS and Linux systems with systemd, unless --no-daemon is specified
 if [[ (! $INPUT_INSTALL_OPTIONS =~ "--no-daemon") && ($OSTYPE =~ darwin || -e /run/systemd/system) ]]; then
+  use_daemon() { true; }
+else
+  use_daemon() { false; }
+fi
+
+if use_daemon; then
   installer_options+=(
     --daemon
     --daemon-user-count "$(python3 -c 'import multiprocessing as mp; print(mp.cpu_count() * 2)')"
@@ -86,7 +94,7 @@ else
 fi
 
 if [[ -n "${INPUT_INSTALL_OPTIONS:-}" ]]; then
-  IFS=' ' read -r -a extra_installer_options <<< "$INPUT_INSTALL_OPTIONS"
+  IFS=' ' read -r -a extra_installer_options <<<"$INPUT_INSTALL_OPTIONS"
   installer_options=("${extra_installer_options[@]}" "${installer_options[@]}")
 fi
 
@@ -95,8 +103,7 @@ echo "installer options: ${installer_options[*]}"
 # There is --retry-on-errors, but only newer curl versions support that
 curl_retries=5
 nix_version=2.31.2
-while ! curl -sS -o "$workdir/install" -v --fail -L "${INPUT_INSTALL_URL:-https://releases.nixos.org/nix/nix-${nix_version}/install}"
-do
+while ! curl -sS -o "$workdir/install" -v --fail -L "${INPUT_INSTALL_URL:-https://releases.nixos.org/nix/nix-${nix_version}/install}"; do
   sleep 1
   ((curl_retries--))
   if [[ $curl_retries -le 0 ]]; then
@@ -107,19 +114,66 @@ done
 
 sh "$workdir/install" "${installer_options[@]}"
 
-# Set paths
-echo "/nix/var/nix/profiles/default/bin" >> "$GITHUB_PATH"
-# new path for nix 2.14
-echo "$HOME/.nix-profile/bin" >> "$GITHUB_PATH"
+# Configure the environment
+#
+# Adapted from the single- and multi-user scripts:
+#   single-user: https://github.com/NixOS/nix/blob/master/scripts/nix-profile-daemon.sh.in
+#   multi-user: https://github.com/NixOS/nix/blob/master/scripts/nix-profile-daemon.sh.in
+#
+# These scripts would normally be evaluated as part of the user's shell profile.
+# GitHub doesn't evaluate profiles or rc scripts by default, so we set up the environment manually.
+echo "::debug::Nix installed, setting up environment"
 
+# Export the path to Nix
 if [[ -n "${INPUT_NIX_PATH:-}" ]]; then
-  echo "NIX_PATH=${INPUT_NIX_PATH}" >> "$GITHUB_ENV"
+  echo "NIX_PATH=${INPUT_NIX_PATH}" >>"$GITHUB_ENV"
 fi
 
-# Set temporary directory (if not already set) to fix https://github.com/cachix/install-nix-action/issues/197
+# Set temporary directory if not already set
+# Fixes https://github.com/cachix/install-nix-action/issues/197
 if [[ -z "${TMPDIR:-}" ]]; then
-  echo "TMPDIR=${RUNNER_TEMP}" >> "$GITHUB_ENV"
+  echo "TMPDIR=${RUNNER_TEMP}" >>"$GITHUB_ENV"
 fi
 
+# Determine NIX_LINK path (XDG spec, newer XDG-compliant, or legacy)
+if [[ -n "${XDG_STATE_HOME:-}" && -e "$XDG_STATE_HOME/nix/profile" ]]; then
+  NIX_LINK="$XDG_STATE_HOME/nix/profile"
+elif [[ -e "$HOME/.local/state/nix/profile" ]]; then
+  NIX_LINK="$HOME/.local/state/nix/profile"
+else
+  NIX_LINK="$HOME/.nix-profile"
+fi
+
+# Set Nix profiles
+echo "NIX_PROFILES=/nix/var/nix/profiles/default $NIX_LINK" >>"$GITHUB_ENV"
+
+# Set NIX_SSL_CERT_FILE if not already configured
+if [[ -z "${NIX_SSL_CERT_FILE:-}" ]]; then
+  # Check common SSL certificate file locations
+  if [[ -f "/etc/ssl/certs/ca-certificates.crt" ]]; then # NixOS, Ubuntu, Debian, Gentoo, Arch
+    echo "NIX_SSL_CERT_FILE=/etc/ssl/certs/ca-certificates.crt" >>"$GITHUB_ENV"
+  elif [[ $OSTYPE =~ darwin && -f "/etc/ssl/cert.pem" ]]; then # macOS
+    echo "NIX_SSL_CERT_FILE=/etc/ssl/cert.pem" >>"$GITHUB_ENV"
+  elif [[ -f "/etc/ssl/ca-bundle.pem" ]]; then # openSUSE Tumbleweed
+    echo "NIX_SSL_CERT_FILE=/etc/ssl/ca-bundle.pem" >>"$GITHUB_ENV"
+  elif [[ -f "/etc/ssl/certs/ca-bundle.crt" ]]; then # Old NixOS
+    echo "NIX_SSL_CERT_FILE=/etc/ssl/certs/ca-bundle.crt" >>"$GITHUB_ENV"
+  elif [[ -f "/etc/pki/tls/certs/ca-bundle.crt" ]]; then # Fedora, CentOS
+    echo "NIX_SSL_CERT_FILE=/etc/pki/tls/certs/ca-bundle.crt" >>"$GITHUB_ENV"
+  elif [[ -f "/nix/var/nix/profiles/default/etc/ssl/certs/ca-bundle.crt" ]]; then # fall back to cacert in default Nix profile
+    echo "NIX_SSL_CERT_FILE=/nix/var/nix/profiles/default/etc/ssl/certs/ca-bundle.crt" >>"$GITHUB_ENV"
+  elif [[ -f "$NIX_LINK/etc/ssl/certs/ca-bundle.crt" ]]; then # fall back to cacert in user Nix profile
+    echo "NIX_SSL_CERT_FILE=$NIX_LINK/etc/ssl/certs/ca-bundle.crt" >>"$GITHUB_ENV"
+  fi
+fi
+
+# Set paths based on the installation type
+if use_daemon; then
+  # Multi-user daemon install - add both paths
+  echo "/nix/var/nix/profiles/default/bin" >>"$GITHUB_PATH"
+fi
+# Always add the user profile path
+echo "$NIX_LINK/bin" >>"$GITHUB_PATH"
+
 # Close the log message group which was opened above
 echo "::endgroup::"
diff --git a/test.nix b/tests/test-build.nix
similarity index 100%
rename from test.nix
rename to tests/test-build.nix
diff --git a/tests/test-env.sh b/tests/test-env.sh
new file mode 100755
index 0000000..3d2e947
--- /dev/null
+++ b/tests/test-env.sh
@@ -0,0 +1,69 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+echo "=== Testing Nix Environment Variables ==="
+echo
+
+# Test NIX_PROFILES
+echo "NIX_PROFILES: ${NIX_PROFILES:-<not set>}"
+if [[ -n "${NIX_PROFILES:-}" ]]; then
+  echo "✓ NIX_PROFILES is set"
+else
+  echo "✗ NIX_PROFILES is not set"
+  exit 1
+fi
+
+# Test NIX_SSL_CERT_FILE
+echo "NIX_SSL_CERT_FILE: ${NIX_SSL_CERT_FILE:-<not set>}"
+if [[ -n "${NIX_SSL_CERT_FILE:-}" ]]; then
+  if [[ -f "$NIX_SSL_CERT_FILE" ]]; then
+    echo "✓ NIX_SSL_CERT_FILE is set and file exists"
+  else
+    echo "✗ NIX_SSL_CERT_FILE is set but file does not exist: $NIX_SSL_CERT_FILE"
+    exit 1
+  fi
+else
+  echo "✗ NIX_SSL_CERT_FILE is not set"
+  exit 1
+fi
+
+# Test PATH contains Nix paths
+echo "PATH: $PATH"
+if echo "$PATH" | grep -E -q "(\.nix-profile|nix/profile)"; then
+  echo "✓ PATH contains Nix paths"
+else
+  echo "✗ PATH does not contain Nix paths"
+  exit 1
+fi
+
+# Test NIX_PATH if set
+if [[ -n "${NIX_PATH:-}" ]]; then
+  echo "NIX_PATH: $NIX_PATH"
+  echo "✓ NIX_PATH is set"
+else
+  echo "NIX_PATH: <not set>"
+  exit 1
+fi
+
+# Test TMPDIR
+echo "TMPDIR: ${TMPDIR:-<not set>}"
+if [[ -n "${TMPDIR:-}" ]]; then
+  echo "✓ TMPDIR is set"
+else
+  echo "⚠ TMPDIR is not set"
+  exit 1
+fi
+
+echo
+echo "=== Testing Nix Command ==="
+if command -v nix >/dev/null 2>&1; then
+  echo "✓ nix command is available"
+  echo "Nix version: $(nix --version)"
+else
+  echo "✗ nix command is not available"
+  exit 1
+fi
+
+echo
+echo "=== Environment Setup Test Complete ==="