diff --git a/run_tests.sh b/run_tests.sh
index f271015f..c2d2cb21 100755
--- a/run_tests.sh
+++ b/run_tests.sh
@@ -53,7 +53,6 @@ function usage {
 #
 root=`pwd -P`
 venv=$root/.venv
-venv_env_version=$venv/environments
 with_venv=tools/with_venv.sh
 included_dirs="sahara_dashboard"
 
@@ -85,6 +84,14 @@ check_only=0
 pseudo=0
 manage=0
 
+# NOTE(tonyb): the release team will automatically update tox.ini to point at
+# the correct requirements branch when creating stable/* from master.  So go to
+# a little effort to get the deault from there to avoid dift and having to
+# update this when branching
+_default_uc=$(sed -n 's/^.*{env:UPPER_CONSTRAINTS_FILE\:\([^}]*\)}.*$/\1/p' \
+              tox.ini | head -n1)
+
+
 # Jenkins sets a "JOB_NAME" variable, if it's not set, we'll make it "default"
 [ "$JOB_NAME" ] || JOB_NAME="default"
 
@@ -211,39 +218,6 @@ function destroy_venv {
   echo "Virtualenv removed."
 }
 
-function environment_check {
-  echo "Checking environment."
-  if [ -f $venv_env_version ]; then
-    set +o errexit
-    cat requirements.txt test-requirements.txt | cmp $venv_env_version - > /dev/null
-    local env_check_result=$?
-    set -o errexit
-    if [ $env_check_result -eq 0 ]; then
-      # If the environment exists and is up-to-date then set our variables
-      command_wrapper="${root}/${with_venv}"
-      echo "Environment is up to date."
-      return 0
-    fi
-  fi
-
-  if [ $always_venv -eq 1 ]; then
-    install_venv
-  else
-    if [ ! -e ${venv} ]; then
-      echo -e "Environment not found. Install? (Y/n) \c"
-    else
-      echo -e "Your environment appears to be out of date. Update? (Y/n) \c"
-    fi
-    read update_env
-    if [ "x$update_env" = "xY" -o "x$update_env" = "x" -o "x$update_env" = "xy" ]; then
-      install_venv
-    else
-      # Set our command wrapper anyway.
-      command_wrapper="${root}/${with_venv}"
-    fi
-  fi
-}
-
 function sanity_check {
   # Anything that should be determined prior to running the tests, server, etc.
   # Don't sanity-check anything environment-related in -N flag is set
@@ -293,6 +267,7 @@ function restore_environment {
 
 function install_venv {
   # Install with install_venv.py
+  export UPPER_CONSTRAINTS_FILE=${UPPER_CONSTRAINTS_FILE:-$_default_uc}
   export PIP_DOWNLOAD_CACHE=${PIP_DOWNLOAD_CACHE-/tmp/.pip_download_cache}
   export PIP_USE_MIRRORS=true
   if [ $quiet -eq 1 ]; then
@@ -305,7 +280,6 @@ function install_venv {
   # Make sure it worked and record the environment version
   sanity_check
   chmod -R 754 $venv
-  cat requirements.txt test-requirements.txt > $venv_env_version
 }
 
 function run_tests {
@@ -473,8 +447,8 @@ if [ $never_venv -eq 0 ]; then
     destroy_venv
   fi
 
-  # Then check if it's up-to-date
-  environment_check
+  # Create or update venv.
+  install_venv
 
   # Create a backup of the up-to-date environment if desired
   if [ $backup_env -eq 1 ]; then
diff --git a/tools/install_venv.py b/tools/install_venv.py
index bcb1f93d..45b6a410 100644
--- a/tools/install_venv.py
+++ b/tools/install_venv.py
@@ -32,7 +32,7 @@ VENV = os.path.join(ROOT, '.venv')
 WITH_VENV = os.path.join(ROOT, 'tools', 'with_venv.sh')
 PIP_REQUIRES = os.path.join(ROOT, 'requirements.txt')
 TEST_REQUIRES = os.path.join(ROOT, 'test-requirements.txt')
-PIP_INSTALL_WRAPPER = os.path.join(ROOT, 'tools', 'pip_install.sh')
+PIP_INSTALL_WRAPPER = os.path.join(ROOT, 'tools', 'tox_install.sh')
 
 
 def die(message, *args):
@@ -110,12 +110,15 @@ def create_virtualenv(venv=VENV):
 
 
 def pip_install(*args):
-    args = [WITH_VENV, 'pip', 'install', '--upgrade'] + list(args)
+    constraints_url = os.environ.get('UPPER_CONSTRAINTS_FILE')
+    args = [WITH_VENV, 'pip', 'install', '-c', constraints_url,
+            '--upgrade'] + list(args)
     run_command(args, redirect_output=False)
 
 
 def pip_install_with_horizon(*args):
-    args = [WITH_VENV, PIP_INSTALL_WRAPPER, 'unconstrained'] + list(args)
+    constraints_url = os.environ.get('UPPER_CONSTRAINTS_FILE')
+    args = [WITH_VENV, PIP_INSTALL_WRAPPER, constraints_url] + list(args)
     run_command(args, redirect_output=False)
 
 
diff --git a/tools/pip_install.sh b/tools/pip_install.sh
deleted file mode 100755
index ad085f40..00000000
--- a/tools/pip_install.sh
+++ /dev/null
@@ -1,66 +0,0 @@
-#!/bin/sh
-
-# The original script is borrowed from neutron-* repos.
-
-# Many of horizon's repos suffer from the problem of depending on horizon,
-# but it not existing on pypi.
-
-# This wrapper for tox's package installer will use the existing package
-# if it exists, else use zuul-cloner if that program exists, else grab it
-# from horizon master via a hard-coded URL. That last case should only
-# happen with devs running unit tests locally.
-
-# From the tox.ini config page:
-# install_command=ARGV
-# default:
-# pip install {opts} {packages}
-
-ZUUL_CLONER=/usr/zuul-env/bin/zuul-cloner
-BRANCH_NAME=master
-horizon_installed=$(echo "import horizon" | python 2>/dev/null ; echo $?)
-
-set -e
-
-zuul_install () {
-    if [ -x "$ZUUL_CLONER" ]; then
-        export ZUUL_BRANCH=${ZUUL_BRANCH-$BRANCH}
-        echo "ZUUL CLONER" > /tmp/tox_install.txt
-        cwd=$(/bin/pwd)
-        cd /tmp
-        $ZUUL_CLONER --cache-dir \
-            /opt/git \
-            --branch $BRANCH_NAME \
-            git://git.openstack.org \
-            openstack/horizon
-        cd openstack/horizon
-        $install_cmd -e .
-        cd "$cwd"
-    else
-        return 1
-    fi
-}
-
-usual_install () {
-    echo "PIP HARDCODE" > /tmp/tox_install.txt
-    if [ -z "$HORIZON_PIP_LOCATION" ]; then
-        HORIZON_PIP_LOCATION="git+https://git.openstack.org/openstack/horizon@$BRANCH_NAME#egg=horizon"
-    fi
-    $install_cmd -U -e ${HORIZON_PIP_LOCATION}
-}
-
-install_cmd="pip install"
-if [ "$1" = "constrained" ]; then
-    install_cmd="$install_cmd $2"
-    shift
-fi
-shift
-
-if [ $horizon_installed -eq 0 ]; then
-    echo "ALREADY INSTALLED" > /tmp/tox_install.txt
-    echo "Horizon already installed; using existing package"
-else
-    zuul_install || usual_install
-fi
-
-$install_cmd -U $*
-exit $?
diff --git a/tools/tox_install.sh b/tools/tox_install.sh
new file mode 100755
index 00000000..20759240
--- /dev/null
+++ b/tools/tox_install.sh
@@ -0,0 +1,85 @@
+#!/usr/bin/env bash
+
+# Client constraint file contains this client version pin that is in conflict
+# with installing the client from source. We should remove the version pin in
+# the constraints file before applying it for from-source installation.
+# The script also has a secondary purpose to install certain special
+# dependencies directly from git.
+
+# Wrapper for pip install that always uses constraints.
+function pip_install() {
+    pip install -c"$localfile" -U "$@"
+}
+
+# Grab the library from git using either zuul-cloner or pip.  The former is
+# there to a take advantage of the setup done by the gate infrastructure
+# and honour any/all Depends-On headers in the commit message
+function install_from_git() {
+    ZUUL_CLONER=/usr/zuul-env/bin/zuul-cloner
+    GIT_HOST=git.openstack.org
+    PROJ=$1
+    EGG=$2
+
+    edit-constraints "$localfile" -- "$EGG"
+    if [ -x "$ZUUL_CLONER" ]; then
+        SRC_DIR="$VIRTUAL_ENV/src"
+        mkdir -p "$SRC_DIR"
+        cd "$SRC_DIR" >/dev/null
+        ZUUL_CACHE_DIR=${ZUUL_CACHE_DIR:-/opt/git} $ZUUL_CLONER \
+            --branch "$BRANCH_NAME" \
+            "git://$GIT_HOST" "$PROJ"
+        pip_install -e "$PROJ/."
+        cd - >/dev/null
+    else
+        pip_install -e"git+https://$GIT_HOST/$PROJ@$BRANCH_NAME#egg=${EGG}"
+    fi
+}
+
+
+
+CONSTRAINTS_FILE="$1"
+shift 1
+
+# This script will either complete with a return code of 0 or the return code
+# of whatever failed.
+set -e
+
+# NOTE(tonyb): Place this in the tox environment's log dir so it will get
+# published to logs.openstack.org for easy debugging.
+mkdir -p "$VIRTUAL_ENV/log/"
+localfile="$VIRTUAL_ENV/log/upper-constraints.txt"
+
+if [[ "$CONSTRAINTS_FILE" != http* ]]; then
+    CONSTRAINTS_FILE="file://$CONSTRAINTS_FILE"
+fi
+# NOTE(tonyb): need to add curl to bindep.txt if the project supports bindep
+curl "$CONSTRAINTS_FILE" --insecure --progress-bar --output "$localfile"
+
+pip_install openstack-requirements
+
+# This is the main purpose of the script: Allow local installation of
+# the current repo. It is listed in constraints file and thus any
+# install will be constrained and we need to unconstrain it.
+edit-constraints "$localfile" -- "$CLIENT_NAME"
+
+declare -a passthrough_args
+while [ $# -gt 0 ] ; do
+    case "$1" in
+    # If we have any special os:<repo_name:<egg_name> deps then process them
+    os:*)
+        declare -a pkg_spec
+        IFS=: pkg_spec=($1)
+        install_from_git "${pkg_spec[1]}" "${pkg_spec[2]}"
+    ;;
+    # Otherwise just pass the other deps through to the constrained pip install
+    *)
+        passthrough_args+=("$1")
+    ;;
+    esac
+    shift 1
+done
+
+# If *only* had special args then then isn't any need to run pip.
+if [ -n "$passthrough_args" ] ; then
+    pip_install "${passthrough_args[@]}"
+fi
diff --git a/tools/with_venv.sh b/tools/with_venv.sh
index 7303990b..15e4cc06 100755
--- a/tools/with_venv.sh
+++ b/tools/with_venv.sh
@@ -4,4 +4,7 @@ VENV_PATH=${VENV_PATH:-${TOOLS_PATH}}
 VENV_DIR=${VENV_NAME:-/../.venv}
 TOOLS=${TOOLS_PATH}
 VENV=${VENV:-${VENV_PATH}/${VENV_DIR}}
+# tools/tox_install.sh looks for VIRTUAL_ENV evrythign else looks for VENV
+# so for now make them the same.
+VIRTUAL_ENV=${VENV:-${VENV_PATH}/${VENV_DIR}}
 source ${VENV}/bin/activate && "$@"
diff --git a/tox.ini b/tox.ini
index bf42dd02..ac2db82f 100644
--- a/tox.ini
+++ b/tox.ini
@@ -5,11 +5,14 @@ skipsdist = True
 
 [testenv]
 usedevelop = True
-install_command = {toxinidir}/tools/pip_install.sh unconstrained {opts} {packages}
+install_command = {toxinidir}/tools/tox_install.sh {env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt} {opts} {packages}
 setenv =
    VIRTUAL_ENV={envdir}
+   BRANCH_NAME=master
+   CLIENT_NAME=sahara-dashboard
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
+       os:openstack/horizon:horizon
 whitelist_externals = /bin/bash
 commands = /bin/bash run_tests.sh -N --no-pep8 {posargs}