diff --git a/ioc/modules/base.nix b/ioc/modules/base.nix
index f777a0a0..4c46eeee 100644
--- a/ioc/modules/base.nix
+++ b/ioc/modules/base.nix
@@ -139,4 +139,14 @@ in {
       }
     ];
   };
+
+  config.nixpkgs.overlays = [
+    (_final: prev: {
+      epnix =
+        prev.epnix
+        // {
+          epics-base = cfg.package;
+        };
+    })
+  ];
 }
diff --git a/ioc/tests/default-ioc/default.nix b/ioc/tests/default-ioc/default.nix
new file mode 100644
index 00000000..0fd66191
--- /dev/null
+++ b/ioc/tests/default-ioc/default.nix
@@ -0,0 +1,44 @@
+releaseBranch: {pkgs, ...}: let
+  inherit (pkgs) epnixLib;
+  inherit (pkgs.stdenv.hostPlatform) system;
+
+  result = epnixLib.evalEpnixModules {
+    nixpkgsConfig.system = system;
+    epnixConfig.imports = [
+      (import ./top/epnix.nix releaseBranch)
+    ];
+  };
+
+  service = result.config.epnix.nixos.services.ioc.config;
+
+  ioc = result.outputs.build;
+in
+  pkgs.nixosTest {
+    name = "default-ioc-epics-base-${releaseBranch}";
+    meta.maintainers = with epnixLib.maintainers; [minijackson];
+
+    nodes.machine = {
+      environment.systemPackages = [pkgs.epnix.epics-base];
+      systemd.services.ioc = service;
+    };
+
+    testScript = ''
+      machine.wait_for_unit("default.target")
+      machine.wait_for_unit("ioc.service")
+
+      with subtest("wait until started"):
+        assert machine.wait_until_succeeds("caget -t SIMPLE:AI").strip() == "0"
+
+      with subtest("EPICS revision is correct"):
+        machine.succeed("journalctl --no-pager -u ioc.service | grep -F '## EPICS R${releaseBranch}'")
+
+      with subtest("ai records"):
+        assert machine.wait_until_succeeds("caget -t SIMPLE:AI").strip() == "0"
+        machine.succeed("caput SIMPLE:AI 123.456")
+        assert machine.wait_until_succeeds("caget -t SIMPLE:AI").strip() == "123.456"
+    '';
+
+    passthru = {
+      inherit ioc;
+    };
+  }
diff --git a/ioc/tests/default-ioc/top/.gitignore b/ioc/tests/default-ioc/top/.gitignore
new file mode 100644
index 00000000..3d648caa
--- /dev/null
+++ b/ioc/tests/default-ioc/top/.gitignore
@@ -0,0 +1,29 @@
+# Install directories
+/bin/
+/cfg/
+/db/
+/dbd/
+/html/
+/include/
+/lib/
+/templates/
+
+# Local configuration files
+/configure/*.local
+
+# iocBoot generated files
+/iocBoot/*ioc*/cdCommands
+/iocBoot/*ioc*/dllPath.bat
+/iocBoot/*ioc*/envPaths
+/iocBoot/*ioc*/relPaths.sh
+
+# Build directories
+O.*/
+
+# Common files created by other tools
+/QtC-*
+/.vscode/
+*.orig
+*.log
+.*.swp
+.DS_Store
diff --git a/ioc/tests/default-ioc/top/Makefile b/ioc/tests/default-ioc/top/Makefile
new file mode 100644
index 00000000..19c9068d
--- /dev/null
+++ b/ioc/tests/default-ioc/top/Makefile
@@ -0,0 +1,31 @@
+# Makefile at top of application tree
+TOP = .
+include $(TOP)/configure/CONFIG
+
+# Directories to build, any order
+DIRS += configure
+DIRS += $(wildcard *Sup)
+DIRS += $(wildcard *App)
+DIRS += $(wildcard *Top)
+DIRS += $(wildcard iocBoot)
+
+# The build order is controlled by these dependency rules:
+
+# All dirs except configure depend on configure
+$(foreach dir, $(filter-out configure, $(DIRS)), \
+    $(eval $(dir)_DEPEND_DIRS += configure))
+
+# Any *App dirs depend on all *Sup dirs
+$(foreach dir, $(filter %App, $(DIRS)), \
+    $(eval $(dir)_DEPEND_DIRS += $(filter %Sup, $(DIRS))))
+
+# Any *Top dirs depend on all *Sup and *App dirs
+$(foreach dir, $(filter %Top, $(DIRS)), \
+    $(eval $(dir)_DEPEND_DIRS += $(filter %Sup %App, $(DIRS))))
+
+# iocBoot depends on all *App dirs
+iocBoot_DEPEND_DIRS += $(filter %App,$(DIRS))
+
+# Add any additional dependency rules here:
+
+include $(TOP)/configure/RULES_TOP
diff --git a/ioc/tests/default-ioc/top/configure/CONFIG b/ioc/tests/default-ioc/top/configure/CONFIG
new file mode 100644
index 00000000..34ace577
--- /dev/null
+++ b/ioc/tests/default-ioc/top/configure/CONFIG
@@ -0,0 +1,45 @@
+# CONFIG - Load build configuration data
+#
+# Do not make changes to this file!
+
+# Allow user to override where the build rules come from
+RULES = $(EPICS_BASE)
+
+# RELEASE files point to other application tops
+include $(TOP)/configure/RELEASE
+-include $(TOP)/configure/RELEASE.$(EPICS_HOST_ARCH).Common
+
+ifdef T_A
+  -include $(TOP)/configure/RELEASE.Common.$(T_A)
+  -include $(TOP)/configure/RELEASE.$(EPICS_HOST_ARCH).$(T_A)
+endif
+
+# Check EPICS_BASE is set properly
+ifneq (file,$(origin EPICS_BASE))
+  $(error EPICS_BASE must be set in a configure/RELEASE file)
+else
+  ifeq ($(wildcard $(EPICS_BASE)/configure/CONFIG_BASE),)
+    $(error EPICS_BASE does not point to an EPICS installation)
+  endif
+endif
+
+CONFIG = $(RULES)/configure
+include $(CONFIG)/CONFIG
+
+# Override the Base definition:
+INSTALL_LOCATION = $(TOP)
+
+# CONFIG_SITE files contain local build configuration settings
+include $(TOP)/configure/CONFIG_SITE
+
+# Host-arch specific settings
+-include $(TOP)/configure/CONFIG_SITE.$(EPICS_HOST_ARCH).Common
+
+ifdef T_A
+  # Target-arch specific settings
+ -include $(TOP)/configure/CONFIG_SITE.Common.$(T_A)
+
+  #  Host & target specific settings
+ -include $(TOP)/configure/CONFIG_SITE.$(EPICS_HOST_ARCH).$(T_A)
+endif
+
diff --git a/ioc/tests/default-ioc/top/configure/CONFIG_SITE b/ioc/tests/default-ioc/top/configure/CONFIG_SITE
new file mode 100644
index 00000000..212485eb
--- /dev/null
+++ b/ioc/tests/default-ioc/top/configure/CONFIG_SITE
@@ -0,0 +1,43 @@
+# CONFIG_SITE
+
+# Make any application-specific changes to the EPICS build
+#   configuration variables in this file.
+#
+# Host/target specific settings can be specified in files named
+#   CONFIG_SITE.$(EPICS_HOST_ARCH).Common
+#   CONFIG_SITE.Common.$(T_A)
+#   CONFIG_SITE.$(EPICS_HOST_ARCH).$(T_A)
+
+# CHECK_RELEASE controls the consistency checking of the support
+#   applications pointed to by the RELEASE* files.
+# Normally CHECK_RELEASE should be set to YES.
+# Set CHECK_RELEASE to NO to disable checking completely.
+# Set CHECK_RELEASE to WARN to perform consistency checking but
+#   continue building even if conflicts are found.
+CHECK_RELEASE = YES
+
+# Set this when you only want to compile this application
+#   for a subset of the cross-compiled target architectures
+#   that Base is built for.
+#CROSS_COMPILER_TARGET_ARCHS = vxWorks-ppc32
+
+# To install files into a location other than $(TOP) define
+#   INSTALL_LOCATION here.
+#INSTALL_LOCATION=</absolute/path/to/install/top>
+
+# Set this when the IOC and build host use different paths
+#   to the install location. This may be needed to boot from
+#   a Microsoft FTP server say, or on some NFS configurations.
+#IOCS_APPL_TOP = </IOC's/absolute/path/to/install/top>
+
+# For application debugging purposes, override the HOST_OPT and/
+#   or CROSS_OPT settings from base/configure/CONFIG_SITE
+#HOST_OPT = NO
+#CROSS_OPT = NO
+
+# These allow developers to override the CONFIG_SITE variable
+# settings without having to modify the configure/CONFIG_SITE
+# file itself.
+-include $(TOP)/../CONFIG_SITE.local
+-include $(TOP)/configure/CONFIG_SITE.local
+
diff --git a/ioc/tests/default-ioc/top/configure/Makefile b/ioc/tests/default-ioc/top/configure/Makefile
new file mode 100644
index 00000000..92543094
--- /dev/null
+++ b/ioc/tests/default-ioc/top/configure/Makefile
@@ -0,0 +1,8 @@
+TOP=..
+
+include $(TOP)/configure/CONFIG
+
+TARGETS = $(CONFIG_TARGETS)
+CONFIGS += $(subst ../,,$(wildcard $(CONFIG_INSTALLS)))
+
+include $(TOP)/configure/RULES
diff --git a/ioc/tests/default-ioc/top/configure/RELEASE b/ioc/tests/default-ioc/top/configure/RELEASE
new file mode 100644
index 00000000..bbcffd23
--- /dev/null
+++ b/ioc/tests/default-ioc/top/configure/RELEASE
@@ -0,0 +1,42 @@
+# RELEASE - Location of external support modules
+#
+# IF YOU CHANGE ANY PATHS in this file or make API changes to
+# any modules it refers to, you should do a "make rebuild" in
+# this application's top level directory.
+#
+# The EPICS build process does not check dependencies against
+# any files from outside the application, so it is safest to
+# rebuild it completely if any modules it depends on change.
+#
+# Host- or target-specific settings can be given in files named
+#  RELEASE.$(EPICS_HOST_ARCH).Common
+#  RELEASE.Common.$(T_A)
+#  RELEASE.$(EPICS_HOST_ARCH).$(T_A)
+#
+# This file is parsed by both GNUmake and an EPICS Perl script,
+# so it may ONLY contain definititions of paths to other support
+# modules, variable definitions that are used in module paths,
+# and include statements that pull in other RELEASE files.
+# Variables may be used before their values have been set.
+# Build variables that are NOT used in paths should be set in
+# the CONFIG_SITE file.
+
+# Variables and paths to dependent modules:
+#MODULES = /path/to/modules
+#MYMODULE = $(MODULES)/my-module
+
+# If using the sequencer, point SNCSEQ at its top directory:
+#SNCSEQ = $(MODULES)/seq-ver
+
+# EPICS_BASE should appear last so earlier modules can override stuff:
+EPICS_BASE = /nix/store/gq8ysfw2yqwij1wd64vcc0nwy8p67vzx-epics-base-7.0.7
+
+# Set RULES here if you want to use build rules from somewhere
+# other than EPICS_BASE:
+#RULES = $(MODULES)/build-rules
+
+# These lines allow developers to override these RELEASE settings
+# without having to modify this file directly.
+-include $(TOP)/../RELEASE.local
+-include $(TOP)/../RELEASE.$(EPICS_HOST_ARCH).local
+-include $(TOP)/configure/RELEASE.local
diff --git a/ioc/tests/default-ioc/top/configure/RULES b/ioc/tests/default-ioc/top/configure/RULES
new file mode 100644
index 00000000..6d56e14e
--- /dev/null
+++ b/ioc/tests/default-ioc/top/configure/RULES
@@ -0,0 +1,6 @@
+# RULES
+
+include $(CONFIG)/RULES
+
+# Library should be rebuilt because LIBOBJS may have changed.
+$(LIBNAME): ../Makefile
diff --git a/ioc/tests/default-ioc/top/configure/RULES.ioc b/ioc/tests/default-ioc/top/configure/RULES.ioc
new file mode 100644
index 00000000..901987c6
--- /dev/null
+++ b/ioc/tests/default-ioc/top/configure/RULES.ioc
@@ -0,0 +1,2 @@
+#RULES.ioc
+include $(CONFIG)/RULES.ioc
diff --git a/ioc/tests/default-ioc/top/configure/RULES_DIRS b/ioc/tests/default-ioc/top/configure/RULES_DIRS
new file mode 100644
index 00000000..3ba269dc
--- /dev/null
+++ b/ioc/tests/default-ioc/top/configure/RULES_DIRS
@@ -0,0 +1,2 @@
+#RULES_DIRS
+include $(CONFIG)/RULES_DIRS
diff --git a/ioc/tests/default-ioc/top/configure/RULES_TOP b/ioc/tests/default-ioc/top/configure/RULES_TOP
new file mode 100644
index 00000000..d09d668d
--- /dev/null
+++ b/ioc/tests/default-ioc/top/configure/RULES_TOP
@@ -0,0 +1,3 @@
+#RULES_TOP
+include $(CONFIG)/RULES_TOP
+
diff --git a/ioc/tests/default-ioc/top/epnix.nix b/ioc/tests/default-ioc/top/epnix.nix
new file mode 100644
index 00000000..582e8ba8
--- /dev/null
+++ b/ioc/tests/default-ioc/top/epnix.nix
@@ -0,0 +1,13 @@
+releaseBranch: _: {
+  epnix = {
+    meta.name = "checks-default-ioc";
+    buildConfig.src = ./.;
+
+    epics-base.releaseBranch = releaseBranch;
+
+    nixos.services.ioc = {
+      app = "simple";
+      ioc = "iocsimple";
+    };
+  };
+}
diff --git a/ioc/tests/default-ioc/top/iocBoot/Makefile b/ioc/tests/default-ioc/top/iocBoot/Makefile
new file mode 100644
index 00000000..91e47d0b
--- /dev/null
+++ b/ioc/tests/default-ioc/top/iocBoot/Makefile
@@ -0,0 +1,6 @@
+TOP = ..
+include $(TOP)/configure/CONFIG
+DIRS += $(wildcard *ioc*)
+DIRS += $(wildcard as*)
+include $(CONFIG)/RULES_DIRS
+
diff --git a/ioc/tests/default-ioc/top/iocBoot/iocsimple/Makefile b/ioc/tests/default-ioc/top/iocBoot/iocsimple/Makefile
new file mode 100644
index 00000000..e1b9aa4a
--- /dev/null
+++ b/ioc/tests/default-ioc/top/iocBoot/iocsimple/Makefile
@@ -0,0 +1,5 @@
+TOP = ../..
+include $(TOP)/configure/CONFIG
+ARCH = $(EPICS_HOST_ARCH)
+TARGETS = envPaths
+include $(TOP)/configure/RULES.ioc
diff --git a/ioc/tests/default-ioc/top/iocBoot/iocsimple/st.cmd b/ioc/tests/default-ioc/top/iocBoot/iocsimple/st.cmd
new file mode 100644
index 00000000..925f14f5
--- /dev/null
+++ b/ioc/tests/default-ioc/top/iocBoot/iocsimple/st.cmd
@@ -0,0 +1,10 @@
+#!../../bin/linux-x86_64/simple
+
+< envPaths
+
+dbLoadDatabase "../../dbd/simple.dbd"
+simple_registerRecordDeviceDriver(pdbbase)
+
+dbLoadRecords("../../db/simple.db")
+
+iocInit()
diff --git a/ioc/tests/default-ioc/top/simpleApp/Db/Makefile b/ioc/tests/default-ioc/top/simpleApp/Db/Makefile
new file mode 100644
index 00000000..3717f9ef
--- /dev/null
+++ b/ioc/tests/default-ioc/top/simpleApp/Db/Makefile
@@ -0,0 +1,11 @@
+TOP=../..
+include $(TOP)/configure/CONFIG
+#----------------------------------------
+#  ADD MACRO DEFINITIONS AFTER THIS LINE
+
+DB += simple.db
+
+include $(TOP)/configure/RULES
+#----------------------------------------
+#  ADD RULES AFTER THIS LINE
+
diff --git a/ioc/tests/default-ioc/top/simpleApp/Db/simple.db b/ioc/tests/default-ioc/top/simpleApp/Db/simple.db
new file mode 100644
index 00000000..ea161887
--- /dev/null
+++ b/ioc/tests/default-ioc/top/simpleApp/Db/simple.db
@@ -0,0 +1,2 @@
+record(ai, "SIMPLE:AI") {
+}
diff --git a/ioc/tests/default-ioc/top/simpleApp/Makefile b/ioc/tests/default-ioc/top/simpleApp/Makefile
new file mode 100644
index 00000000..60ab8ae8
--- /dev/null
+++ b/ioc/tests/default-ioc/top/simpleApp/Makefile
@@ -0,0 +1,14 @@
+# Makefile at top of application tree
+TOP = ..
+include $(TOP)/configure/CONFIG
+
+# Directories to be built, in any order.
+# You can replace these wildcards with an explicit list
+DIRS += $(wildcard src* *Src*)
+DIRS += $(wildcard db* *Db*)
+
+# If the build order matters, add dependency rules like this,
+# which specifies that xxxSrc must be built after src:
+#xxxSrc_DEPEND_DIRS += src
+
+include $(TOP)/configure/RULES_DIRS
diff --git a/ioc/tests/default-ioc/top/simpleApp/src/Makefile b/ioc/tests/default-ioc/top/simpleApp/src/Makefile
new file mode 100644
index 00000000..483225ad
--- /dev/null
+++ b/ioc/tests/default-ioc/top/simpleApp/src/Makefile
@@ -0,0 +1,29 @@
+TOP=../..
+
+include $(TOP)/configure/CONFIG
+#----------------------------------------
+#  ADD MACRO DEFINITIONS AFTER THIS LINE
+#=============================
+
+PROD_IOC = simple
+# simple.dbd will be created and installed
+DBD += simple.dbd
+
+# simple.dbd will be made up from these files:
+simple_DBD += base.dbd
+
+# simple_registerRecordDeviceDriver.cpp derives from simple.dbd
+simple_SRCS += simple_registerRecordDeviceDriver.cpp
+
+# Build the main IOC entry point on workstation OSs.
+simple_SRCS_DEFAULT += simpleMain.cpp
+
+# Finally link to the EPICS Base libraries
+simple_LIBS += $(EPICS_BASE_IOC_LIBS)
+
+#===========================
+
+include $(TOP)/configure/RULES
+#----------------------------------------
+#  ADD RULES AFTER THIS LINE
+
diff --git a/ioc/tests/default-ioc/top/simpleApp/src/simpleMain.cpp b/ioc/tests/default-ioc/top/simpleApp/src/simpleMain.cpp
new file mode 100644
index 00000000..e4e5e3b2
--- /dev/null
+++ b/ioc/tests/default-ioc/top/simpleApp/src/simpleMain.cpp
@@ -0,0 +1,23 @@
+/* simpleMain.cpp */
+/* Author:  Marty Kraimer Date:    17MAR2000 */
+
+#include <stddef.h>
+#include <stdlib.h>
+#include <stddef.h>
+#include <string.h>
+#include <stdio.h>
+
+#include "epicsExit.h"
+#include "epicsThread.h"
+#include "iocsh.h"
+
+int main(int argc,char *argv[])
+{
+    if(argc>=2) {
+        iocsh(argv[1]);
+        epicsThreadSleep(.2);
+    }
+    iocsh(NULL);
+    epicsExit(0);
+    return(0);
+}
diff --git a/ioc/tests/default.nix b/ioc/tests/default.nix
index 563fac86..62ca3c65 100644
--- a/ioc/tests/default.nix
+++ b/ioc/tests/default.nix
@@ -1,6 +1,9 @@
 {pkgs, ...} @ args:
 with pkgs.lib;
   {
+    default-ioc-epics-base-3 = import ./default-ioc "3" args;
+    default-ioc-epics-base-7 = import ./default-ioc "7" args;
+
     support-seq-simple = import ./support/seq/simple args;
     support-StreamDevice-simple = import ./support/StreamDevice/simple args;
     support-autosave-simple = import ./support/autosave/simple args;