diff --git a/au/code/au/CMakeLists.txt b/au/code/au/CMakeLists.txt
index 3973077..74351bf 100644
--- a/au/code/au/CMakeLists.txt
+++ b/au/code/au/CMakeLists.txt
@@ -21,144 +21,31 @@ include("${PROJECT_SOURCE_DIR}/cmake/HeaderOnlyLibrary.cmake")
 header_only_library(
   NAME au
   HEADERS
+    apply_magnitude.hh
+    apply_rational_magnitude_to_integral.hh
     au.hh
-  DEPS
-    chrono_interop
-    constant
-    math
-  GTEST_SRCS
-    au_test.cc
-  GTEST_EXTRA_DEPS
-    testing
-)
-
-header_only_library(
-  NAME chrono_interop
-  HEADERS
     chrono_interop.hh
-  DEPS
-    prefix
-    quantity
-    units
-  GTEST_SRCS
-    chrono_interop_test.cc
-  GTEST_EXTRA_DEPS
-    prefix
-    testing
-)
-
-header_only_library(
-  NAME constant
-  HEADERS
     constant.hh
-  DEPS
-    quantity
-    unit_of_measure
-    wrapper_operations
-  GTEST_SRCS
-    constant_test.cc
-  GTEST_EXTRA_DEPS
-    chrono_interop
-    testing
-    units
-)
-
-header_only_library(
-  NAME io
-  HEADERS
+    conversion_policy.hh
+    dimension.hh
     io.hh
-  DEPS
-    quantity
-    quantity_point
-    zero
-  GTEST_SRCS
-    io_test.cc
-  GTEST_EXTRA_DEPS
-    prefix
-)
-
-header_only_library(
-  NAME math
-  HEADERS
+    magnitude.hh
     math.hh
-  DEPS
-    constant
-    quantity
-    quantity_point
-    units
-  GTEST_SRCS
-    math_test.cc
-  GTEST_EXTRA_DEPS
-    testing
-)
-
-header_only_library(
-  NAME prefix
-  HEADERS
+    operators.hh
+    packs.hh
+    power_aliases.hh
     prefix.hh
-  DEPS
-    quantity
-    quantity_point
-    unit_of_measure
-    unit_symbol
-  GTEST_SRCS
-    prefix_test.cc
-  GTEST_EXTRA_DEPS
-    testing
-)
-
-header_only_library(
-  NAME quantity
-  HEADERS
     quantity.hh
-  DEPS
-    apply_magnitude
-    conversion_policy
-    operators
-    rep
-    unit_of_measure
-    utility
-    zero
-  GTEST_SRCS
-    quantity_chrono_policy_correspondence_test.cc
-    quantity_test.cc
-  GTEST_EXTRA_DEPS
-    chrono_policy_validation
-    prefix
-    testing
-)
-
-header_only_library(
-  NAME quantity_point
-  HEADERS
     quantity_point.hh
-  DEPS
-    quantity
-    stdx
-    utility
-  GTEST_SRCS
-    quantity_point_test.cc
-  GTEST_EXTRA_DEPS
-    prefix
-    testing
-)
-
-header_only_library(
-  NAME testing
-  HEADERS
-    testing.hh
-  DEPS
-    io
-    stdx
-    unit_of_measure
-    GTest::gmock
-  GTEST_SRCS
-    testing_test.cc
-)
-
-header_only_library(
-  NAME units
-  HEADERS
+    rep.hh
+    unit_of_measure.hh
+    unit_symbol.hh
+    wrapper_operations.hh
+    zero.hh
+    stdx/experimental/is_detected.hh
+    stdx/functional.hh
+    stdx/type_traits.hh
+    stdx/utility.hh
     units/amperes.hh
     units/bars.hh
     units/becquerel.hh
@@ -211,13 +98,121 @@ header_only_library(
     units/watts.hh
     units/webers.hh
     units/yards.hh
+    utility/factoring.hh
+    utility/string_constant.hh
+    utility/type_traits.hh
+)
+
+header_only_library(
+  NAME testing
+  HEADERS testing.hh
+  DEPS
+    au
+    GTest::gmock
+)
+
+#
+# Private implementation detail targets
+#
+
+header_only_library(
+  NAME chrono_policy_validation
+  INTERNAL_ONLY
+  HEADERS chrono_policy_validation.hh
+  DEPS
+    au
+    GTest::gtest
+)
+
+#
+# Tests
+#
+
+gtest_based_test(
+  NAME au_test
+  SRCS
+    au_test.cc
+  DEPS
+    au
+    testing
+)
+
+gtest_based_test(
+  NAME chrono_interop_test
+  SRCS
+    chrono_interop_test.cc
+  DEPS
+    au
+    testing
+)
+
+gtest_based_test(
+  NAME constant_test
+  SRCS
+    constant_test.cc
+  DEPS
+    au
+    testing
+)
+
+gtest_based_test(
+  NAME io_test
+  SRCS
+    io_test.cc
+  DEPS
+    au
+)
+
+gtest_based_test(
+  NAME math_test
+  SRCS
+    math_test.cc
   DEPS
-    prefix
-    quantity
-    quantity_point
-    unit_of_measure
-    unit_symbol
-  GTEST_SRCS
+    au
+    testing
+)
+
+gtest_based_test(
+  NAME prefix_test
+  SRCS
+    prefix_test.cc
+  DEPS
+    au
+    testing
+)
+
+gtest_based_test(
+  NAME quantity_test
+  SRCS
+    quantity_chrono_policy_correspondence_test.cc
+    quantity_test.cc
+  DEPS
+    au
+    chrono_policy_validation
+    testing
+)
+
+gtest_based_test(
+  NAME quantity_point_test
+  SRCS
+    quantity_point_test.cc
+  DEPS
+    au
+    testing
+)
+
+gtest_based_test(
+  NAME testing_test
+  SRCS
+    testing_test.cc
+  DEPS
+    au
+    testing
+)
+
+gtest_based_test(
+  NAME units_test
+  SRCS
     units/test/amperes_test.cc
     units/test/bars_test.cc
     units/test/becquerel_test.cc
@@ -270,238 +265,153 @@ header_only_library(
     units/test/watts_test.cc
     units/test/webers_test.cc
     units/test/yards_test.cc
-  GTEST_EXTRA_DEPS
+  DEPS
+    au
     testing
 )
 
-header_only_library(
-  NAME unit_symbol
-  HEADERS
-    unit_symbol.hh
-  DEPS
-    wrapper_operations
-  GTEST_SRCS
+gtest_based_test(
+  NAME unit_symbol_test
+  SRCS
     unit_symbol_test.cc
-  GTEST_EXTRA_DEPS
+  DEPS
+    au
     testing
-    units
 )
 
 #
 # Private implementation detail targets
 #
 
-header_only_library(
-  NAME apply_magnitude
-  INTERNAL_ONLY
-  HEADERS
-    apply_magnitude.hh
-  DEPS
-    apply_rational_magnitude_to_integral
-  GTEST_SRCS
+gtest_based_test(
+  NAME apply_magnitude_test
+  SRCS
     apply_magnitude_test.cc
-  GTEST_EXTRA_DEPS
+  DEPS
+    au
     testing
 )
 
-header_only_library(
-  NAME apply_rational_magnitude_to_integral
-  INTERNAL_ONLY
-  HEADERS
-    apply_rational_magnitude_to_integral.hh
-  DEPS
-    magnitude
-  GTEST_SRCS
+gtest_based_test(
+  NAME apply_rational_magnitude_to_integral_test
+  SRCS
     apply_rational_magnitude_to_integral_test.cc
-  GTEST_EXTRA_DEPS
+  DEPS
+    au
     testing
 )
 
-header_only_library(
-  NAME chrono_policy_validation
-  INTERNAL_ONLY
-  HEADERS
-    chrono_policy_validation.hh
-  DEPS
-    dimension
-    quantity
-    stdx
-    unit_of_measure
-    GTest::gtest
-  GTEST_SRCS
+gtest_based_test(
+  NAME chrono_policy_validation_test
+  SRCS
     chrono_policy_validation_test.cc
-  GTEST_EXTRA_DEPS
-    prefix
+  DEPS
+    au
+    chrono_policy_validation
     testing
 )
 
 
-header_only_library(
-  NAME conversion_policy
-  INTERNAL_ONLY
-  HEADERS
-    conversion_policy.hh
-  DEPS
-    magnitude
-    stdx
-    unit_of_measure
-  GTEST_SRCS
+gtest_based_test(
+  NAME conversion_policy_test
+  SRCS
     conversion_policy_test.cc
+  DEPS
+    au
+    testing
 )
 
-header_only_library(
-  NAME dimension
-  INTERNAL_ONLY
-  HEADERS
-    dimension.hh
-  DEPS
-    packs
-    power_aliases
-  GTEST_SRCS
+gtest_based_test(
+  NAME dimension_test
+  SRCS
     dimension_test.cc
-  GTEST_EXTRA_DEPS
+  DEPS
+    au
     testing
-    units
 )
 
-header_only_library(
-  NAME magnitude
-  INTERNAL_ONLY
-  HEADERS
-    magnitude.hh
-  DEPS
-    packs
-    power_aliases
-    stdx
-    utility
-    zero
-  GTEST_SRCS
+gtest_based_test(
+  NAME magnitude_test
+  SRCS
     magnitude_test.cc
-  GTEST_EXTRA_DEPS
+  DEPS
+    au
     testing
 )
 
-header_only_library(
-  NAME operators
-  INTERNAL_ONLY
-  HEADERS
-    operators.hh
-  GTEST_SRCS
+gtest_based_test(
+  NAME operators_test
+  SRCS
     operators_test.cc
-  GTEST_EXTRA_DEPS
+  DEPS
     testing
 )
 
-header_only_library(
-  NAME packs
-  INTERNAL_ONLY
-  HEADERS
-    packs.hh
-  DEPS
-    stdx
-    utility
-  GTEST_SRCS
+gtest_based_test(
+  NAME packs_test
+  SRCS
     packs_test.cc
+  DEPS
+    au
 )
 
-header_only_library(
-  NAME power_aliases
-  INTERNAL_ONLY
-  HEADERS
-    power_aliases.hh
-  GTEST_SRCS
+gtest_based_test(
+  NAME power_aliases_test
+  SRCS
     power_aliases_test.cc
-  GTEST_EXTRA_DEPS
-    packs
+  DEPS
+    au
 )
 
-header_only_library(
-  NAME rep
-  INTERNAL_ONLY
-  HEADERS
-    rep.hh
-  DEPS
-    stdx
-  GTEST_SRCS
+gtest_based_test(
+  NAME rep_test
+  SRCS
     rep_test.cc
-  GTEST_EXTRA_DEPS
-    chrono_interop
-    constant
-    magnitude
-    prefix
-    quantity
-    quantity_point
-    unit_symbol
-    units
+  DEPS
+    au
 )
 
-header_only_library(
-  NAME stdx
-  INTERNAL_ONLY
-  HEADERS
-    stdx/experimental/is_detected.hh
-    stdx/functional.hh
-    stdx/type_traits.hh
-    stdx/utility.hh
-  GTEST_SRCS
+gtest_based_test(
+  NAME stdx_test
+  SRCS
     stdx/test/utility_test.cc
+  DEPS
+    au
 )
 
-header_only_library(
-  NAME unit_of_measure
-  INTERNAL_ONLY
-  HEADERS
-    unit_of_measure.hh
-  DEPS
-    dimension
-    magnitude
-    power_aliases
-    stdx
-    utility
-    zero
-  GTEST_SRCS
+gtest_based_test(
+  NAME unit_of_measure_test
+  SRCS
     unit_of_measure_test.cc
-  GTEST_EXTRA_DEPS
-    prefix
+  DEPS
+    au
     testing
-    units
 )
 
-header_only_library(
-  NAME utility
-  INTERNAL_ONLY
-  HEADERS
-    utility/factoring.hh
-    utility/string_constant.hh
-    utility/type_traits.hh
-  DEPS
-    stdx
-  GTEST_SRCS
+gtest_based_test(
+  NAME utility_test
+  SRCS
     utility/test/factoring_test.cc
     utility/test/string_constant_test.cc
     utility/test/type_traits_test.cc
+  DEPS
+    au
+    testing
 )
 
-header_only_library(
-  NAME wrapper_operations
-  INTERNAL_ONLY
-  HEADERS
-    wrapper_operations.hh
-  DEPS
-    quantity
-    stdx
-  GTEST_SRCS
+gtest_based_test(
+  NAME wrapper_operations_test
+  SRCS
     wrapper_operations_test.cc
-  GTEST_EXTRA_DEPS
+  DEPS
+    au
     testing
-    units
 )
 
-header_only_library(
-  NAME zero
-  INTERNAL_ONLY
-  HEADERS
-    zero.hh
-  GTEST_SRCS
+gtest_based_test(
+  NAME zero_test
+  SRCS
     zero_test.cc
+  DEPS
+    au
 )
diff --git a/cmake/HeaderOnlyLibrary.cmake b/cmake/HeaderOnlyLibrary.cmake
index 28daf00..3c49527 100644
--- a/cmake/HeaderOnlyLibrary.cmake
+++ b/cmake/HeaderOnlyLibrary.cmake
@@ -23,8 +23,6 @@ function(header_only_library)
   set(multiValueVars
     HEADERS
     DEPS
-    GTEST_SRCS
-    GTEST_EXTRA_DEPS
   )
 
   cmake_parse_arguments(
@@ -73,18 +71,40 @@ function(header_only_library)
     FILE_SET HEADERS
     INCLUDES DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}"
   )
+endfunction()
 
-  # Add the test, if requested.
-  if (DEFINED ARG_GTEST_SRCS)
-    add_executable("${ARG_NAME}_test")
-    target_sources("${ARG_NAME}_test" PRIVATE ${ARG_GTEST_SRCS})
-    target_link_libraries(
-      "${ARG_NAME}_test"
-      PRIVATE
-      ${ARG_NAME}
-      ${ARG_GTEST_EXTRA_DEPS}
-      GTest::gmock_main
-    )
-    gtest_discover_tests("${ARG_NAME}_test")
-  endif()
+function(gtest_based_test)
+  #
+  # Handle argument parsing
+  #
+
+  set(prefix ARG)
+  set(singleValueVars NAME)
+  set(multiValueVars
+    SRCS
+    DEPS
+  )
+
+  cmake_parse_arguments(
+    PARSE_ARGV 0
+    "${prefix}"
+    "${noValueVars}"
+    "${singleValueVars}"
+    "${multiValueVars}"
+  )
+
+  #
+  # Function body
+  #
+
+  # Add the test.
+  add_executable(${ARG_NAME})
+  target_sources(${ARG_NAME} PRIVATE ${ARG_SRCS})
+  target_link_libraries(
+    ${ARG_NAME}
+    PRIVATE
+    ${ARG_DEPS}
+    GTest::gmock_main
+  )
+  gtest_discover_tests(${ARG_NAME})
 endfunction()
diff --git a/docs/install.md b/docs/install.md
index a862d3a..99f0cf9 100644
--- a/docs/install.md
+++ b/docs/install.md
@@ -267,8 +267,7 @@ In either case, here are the main targets and include files provided by the Au l
 
 | Target | Headers provided | Notes |
 |--------|------------------|-------|
-| `Au::au` | `"au/au.hh"`<br>`"au/units/*.hh"` | Core library functionality.  See [all available units](https://github.com/aurora-opensource/au/tree/main/au/units) |
-| `Au::io` | `"au/io.hh"` | `operator<<` support |
+| `Au::au` | `"au/au.hh"`<br>`"au/io.hh"`<br>`"au/units/*.hh"` | Core library functionality.  See [all available units](https://github.com/aurora-opensource/au/tree/main/au/units) |
 | `Au::testing` | `"au/testing.hh"` | Utilities for writing googletest tests |
 
 !!! note
@@ -293,8 +292,8 @@ In either case, here are the main targets and include files provided by the Au l
     FetchContent_MakeAvailable(Au)
     ```
 
-    You should now be able to depend on Au targets, such as `Au::au` or `Au::io`, and include their
-    corresponding headers, such as `#include "au/au.hh"` or `#include "au/io.hh"`.
+    You should now be able to depend on Au targets, such as `Au::au` or `Au::testing`, and include
+    headers from them, such as `#include "au/au.hh"` or `#include "au/testing.hh"`.
 
 === "Using `find_package`"
     Before you can use `find_package`, you need to install the library to your system.  This means