CTest: add an ENVIRONMENT_MODIFICATION property

This property allows projects to modify environment variables at test
time rather than trying to guess what the state should be based on what
is present at configure time. Of particular interest is the ability to
use a `PATH` present at test time while adding entries known to be
necessary for the test itself.

There are multiple operations provided to modify variables, including:

  - setting and unsetting
  - appending and prepending as:
    - strings
    - path lists
    - CMake lists

Additionally, a `reset` action is provided to cancel any prior
modifications to that particular variable in the case of incremental
additions to the test property.

24 files changed, 339 insertions, 3 deletions

diff --git a/Auxiliary/vim/syntax/cmake.vim b/Auxiliary/vim/syntax/cmake.vim
index d2a04fe..f936ca0 100644
--- a/Auxiliary/vim/syntax/cmake.vim
+++ b/Auxiliary/vim/syntax/cmake.vim
@@ -160,6 +160,7 @@ syn keyword cmakeProperty contained
             \ ENABLED_LANGUAGES
             \ ENABLE_EXPORTS
             \ ENVIRONMENT
+            \ ENVIRONMENT_MODIFICATION
             \ EXCLUDE_FROM_ALL
             \ EXCLUDE_FROM_DEFAULT_BUILD
             \ EXPORT_NAME
diff --git a/Help/manual/cmake-properties.7.rst b/Help/manual/cmake-properties.7.rst
index 4212913..c71e8ff 100644
--- a/Help/manual/cmake-properties.7.rst
+++ b/Help/manual/cmake-properties.7.rst
@@ -451,6 +451,7 @@ Properties on Tests
    /prop_test/DEPENDS
    /prop_test/DISABLED
    /prop_test/ENVIRONMENT
+   /prop_test/ENVIRONMENT_MODIFICATION
    /prop_test/FAIL_REGULAR_EXPRESSION
    /prop_test/FIXTURES_CLEANUP
    /prop_test/FIXTURES_REQUIRED
diff --git a/Help/prop_test/ENVIRONMENT_MODIFICATION.rst b/Help/prop_test/ENVIRONMENT_MODIFICATION.rst
new file mode 100644
index 0000000..ffd5de4
--- /dev/null
+++ b/Help/prop_test/ENVIRONMENT_MODIFICATION.rst
@@ -0,0 +1,33 @@
+ENVIRONMENT_MODIFICATION
+------------------------
+
+Specify environment variables that should be modified for running a test. Note
+that the operations performed by this property are performed after the
+:prop_test:`ENVIRONMENT` property is already applied.
+
+If set to a list of environment variables and values of the form
+``MYVAR=OP:VALUE``. Entries are considered in the order specified in the
+property's value. The ``OP`` may be one of:
+
+  - ``reset``: Reset to the unmodified value, ignoring all modifications to
+    ``MYVAR`` prior to this entry. Note that this will reset the variable to
+    the value set by :prop_test:`ENVIRONMENT`, if it was set, and otherwise
+    to its state from the rest of the CTest execution.
+  - ``set``: Replaces the current value of ``MYVAR`` with ``VALUE``.
+  - ``unset``: Unsets the current value of ``MYVAR``.
+  - ``string_append``: Appends ``VALUE`` to the current value of ``MYVAR``.
+  - ``string_prepend``: Prepends ``VALUE`` to the current value of ``MYVAR``.
+  - ``path_list_append``: Appends ``VALUE`` to the current value of ``MYVAR``
+    using the platform-specific list separator.
+  - ``path_list_prepend``: Prepends ``VALUE`` to the current value of
+    ``MYVAR`` using the platform-specific list separator.
+  - ``cmake_list_append``: Appends ``VALUE`` to the current value of ``MYVAR``
+    using ``;`` as the separator.
+  - ``cmake_list_prepend``: Prepends ``VALUE`` to the current value of
+    ``MYVAR`` using ``;`` as the separator.
+
+Unrecognized ``OP`` values will result in the test failing before it is
+executed. This is so that future operations may be added without changing
+valid behavior of existing tests.
+
+The environment changes from this property do not affect other tests.
diff --git a/Help/release/dev/ctest-environment-modifications.rst b/Help/release/dev/ctest-environment-modifications.rst
new file mode 100644
index 0000000..64265f0
--- /dev/null
+++ b/Help/release/dev/ctest-environment-modifications.rst
@@ -0,0 +1,7 @@
+ctest-environment-modifications
+-------------------------------
+
+* :manual:`ctest(1)` learned to be able to modify the environment for a test
+  through the :prop_test:`ENVIRONMENT_MODIFICATION` property. This is allows
+  for updates to environment variables based on the environment present at
+  test time.
diff --git a/Source/CTest/cmCTestMultiProcessHandler.cxx b/Source/CTest/cmCTestMultiProcessHandler.cxx
index 86a8e00..d90c4a6 100644
--- a/Source/CTest/cmCTestMultiProcessHandler.cxx
+++ b/Source/CTest/cmCTestMultiProcessHandler.cxx
@@ -1026,6 +1026,11 @@ static Json::Value DumpCTestProperties(
     properties.append(DumpCTestProperty(
       "ENVIRONMENT", DumpToJsonArray(testProperties.Environment)));
   }
+  if (!testProperties.EnvironmentModification.empty()) {
+    properties.append(DumpCTestProperty(
+      "ENVIRONMENT_MODIFICATION",
+      DumpToJsonArray(testProperties.EnvironmentModification)));
+  }
   if (!testProperties.ErrorRegularExpressions.empty()) {
     properties.append(DumpCTestProperty(
       "FAIL_REGULAR_EXPRESSION",
diff --git a/Source/CTest/cmCTestRunTest.cxx b/Source/CTest/cmCTestRunTest.cxx
index 4e9b0f0..20f0ed3 100644
--- a/Source/CTest/cmCTestRunTest.cxx
+++ b/Source/CTest/cmCTestRunTest.cxx
@@ -8,12 +8,16 @@
 #include <cstdint>
 #include <cstdio>
 #include <cstring>
+#include <functional>
 #include <iomanip>
 #include <ratio>
 #include <sstream>
 #include <utility>
 
 #include <cm/memory>
+#include <cm/optional>
+#include <cm/string_view>
+#include <cmext/string_view>
 
 #include "cmsys/RegularExpression.hxx"
 
@@ -640,6 +644,7 @@ bool cmCTestRunTest::StartTest(size_t completed, size_t total)
 
   return this->ForkProcess(timeout, this->TestProperties->ExplicitTimeout,
                            &this->TestProperties->Environment,
+                           &this->TestProperties->EnvironmentModification,
                            &this->TestProperties->Affinity);
 }
 
@@ -696,6 +701,17 @@ void cmCTestRunTest::ComputeArguments()
     cmCTestLog(this->CTest, HANDLER_VERBOSE_OUTPUT,
                this->Index << ":  " << env << std::endl);
   }
+  if (!this->TestProperties->EnvironmentModification.empty()) {
+    cmCTestLog(this->CTest, HANDLER_VERBOSE_OUTPUT,
+               this->Index << ": "
+                           << "Environment variable modifications: "
+                           << std::endl);
+  }
+  for (std::string const& envmod :
+       this->TestProperties->EnvironmentModification) {
+    cmCTestLog(this->CTest, HANDLER_VERBOSE_OUTPUT,
+               this->Index << ":  " << envmod << std::endl);
+  }
 }
 
 void cmCTestRunTest::ParseOutputForMeasurements()
@@ -719,9 +735,11 @@ void cmCTestRunTest::ParseOutputForMeasurements()
   }
 }
 
-bool cmCTestRunTest::ForkProcess(cmDuration testTimeOut, bool explicitTimeout,
-                                 std::vector<std::string>* environment,
-                                 std::vector<size_t>* affinity)
+bool cmCTestRunTest::ForkProcess(
+  cmDuration testTimeOut, bool explicitTimeout,
+  std::vector<std::string>* environment,
+  std::vector<std::string>* environment_modification,
+  std::vector<size_t>* affinity)
 {
   this->TestProcess->SetId(this->Index);
   this->TestProcess->SetWorkingDirectory(this->TestProperties->Directory);
@@ -770,6 +788,127 @@ bool cmCTestRunTest::ForkProcess(cmDuration testTimeOut, bool explicitTimeout,
     }
   }
 
+  if (environment_modification && !environment_modification->empty()) {
+    std::map<std::string, cm::optional<std::string>> env_application;
+
+#ifdef _WIN32
+    char path_sep = ';';
+#else
+    char path_sep = ':';
+#endif
+
+    auto apply_diff =
+      [&env_application](const std::string& name,
+                         std::function<void(std::string&)> const& apply) {
+        auto entry = env_application.find(name);
+        std::string output;
+        if (entry != env_application.end() && entry->second) {
+          output = *entry->second;
+        }
+        apply(output);
+        entry->second = output;
+      };
+
+    bool err_occurred = false;
+
+    for (auto const& envmod : *environment_modification) {
+      // Split on `=`
+      auto const eq_loc = envmod.find_first_of('=');
+      if (eq_loc == std::string::npos) {
+        cmCTestLog(this->CTest, ERROR_MESSAGE,
+                   "Error: Missing `=` after the variable name in: "
+                     << envmod << std::endl);
+        err_occurred = true;
+        continue;
+      }
+      auto const name = envmod.substr(0, eq_loc);
+
+      // Split value on `:`
+      auto const op_value_start = eq_loc + 1;
+      auto const colon_loc = envmod.find_first_of(':', op_value_start);
+      if (colon_loc == std::string::npos) {
+        cmCTestLog(this->CTest, ERROR_MESSAGE,
+                   "Error: Missing `:` after the operation in: " << envmod
+                                                                 << std::endl);
+        err_occurred = true;
+        continue;
+      }
+      auto const op =
+        envmod.substr(op_value_start, colon_loc - op_value_start);
+
+      auto const value_start = colon_loc + 1;
+      auto const value = envmod.substr(value_start);
+
+      // Determine what to do with the operation.
+      if (op == "reset"_s) {
+        auto entry = env_application.find(name);
+        if (entry != env_application.end()) {
+          env_application.erase(entry);
+        }
+      } else if (op == "set"_s) {
+        env_application[name] = value;
+      } else if (op == "unset"_s) {
+        env_application[name] = {};
+      } else if (op == "string_append"_s) {
+        apply_diff(name, [&value](std::string& output) { output += value; });
+      } else if (op == "string_prepend"_s) {
+        apply_diff(name,
+                   [&value](std::string& output) { output.insert(0, value); });
+      } else if (op == "path_list_append"_s) {
+        apply_diff(name, [&value, path_sep](std::string& output) {
+          if (!output.empty()) {
+            output += path_sep;
+          }
+          output += value;
+        });
+      } else if (op == "path_list_prepend"_s) {
+        apply_diff(name, [&value, path_sep](std::string& output) {
+          if (!output.empty()) {
+            output.insert(output.begin(), path_sep);
+          }
+          output.insert(0, value);
+        });
+      } else if (op == "cmake_list_append"_s) {
+        apply_diff(name, [&value](std::string& output) {
+          if (!output.empty()) {
+            output += ';';
+          }
+          output += value;
+        });
+      } else if (op == "cmake_list_prepend"_s) {
+        apply_diff(name, [&value](std::string& output) {
+          if (!output.empty()) {
+            output.insert(output.begin(), ';');
+          }
+          output.insert(0, value);
+        });
+      } else {
+        cmCTestLog(this->CTest, ERROR_MESSAGE,
+                   "Error: Unrecognized environment manipulation argument: "
+                     << op << std::endl);
+        err_occurred = true;
+        continue;
+      }
+    }
+
+    if (err_occurred) {
+      return false;
+    }
+
+    for (auto const& env_apply : env_application) {
+      if (env_apply.second) {
+        auto const env_update =
+          cmStrCat(env_apply.first, '=', *env_apply.second);
+        cmSystemTools::PutEnv(env_update);
+        envMeasurement << env_update << std::endl;
+      } else {
+        cmSystemTools::UnsetEnv(env_apply.first.c_str());
+        // Signify that this variable is being actively unset
+        envMeasurement << "#" << env_apply.first << "=" << std::endl;
+      }
+    }
+  }
+
   if (this->UseAllocatedResources) {
     std::vector<std::string> envLog;
     this->SetupResourcesEnvironment(&envLog);
diff --git a/Source/CTest/cmCTestRunTest.h b/Source/CTest/cmCTestRunTest.h
index a4981c3..2082156 100644
--- a/Source/CTest/cmCTestRunTest.h
+++ b/Source/CTest/cmCTestRunTest.h
@@ -113,6 +113,7 @@ private:
   void ExeNotFound(std::string exe);
   bool ForkProcess(cmDuration testTimeOut, bool explicitTimeout,
                    std::vector<std::string>* environment,
+                   std::vector<std::string>* environment_modification,
                    std::vector<size_t>* affinity);
   void WriteLogOutputTop(size_t completed, size_t total);
   // Run post processing of the process output for MemCheck
diff --git a/Source/CTest/cmCTestTestHandler.cxx b/Source/CTest/cmCTestTestHandler.cxx
index 72b86c1..c29c124 100644
--- a/Source/CTest/cmCTestTestHandler.cxx
+++ b/Source/CTest/cmCTestTestHandler.cxx
@@ -2245,6 +2245,8 @@ bool cmCTestTestHandler::SetTestsProperties(
             cmExpandList(val, rt.Depends);
           } else if (key == "ENVIRONMENT"_s) {
             cmExpandList(val, rt.Environment);
+          } else if (key == "ENVIRONMENT_MODIFICATION"_s) {
+            cmExpandList(val, rt.EnvironmentModification);
           } else if (key == "LABELS"_s) {
             std::vector<std::string> Labels = cmExpandedList(val);
             rt.Labels.insert(rt.Labels.end(), Labels.begin(), Labels.end());
diff --git a/Source/CTest/cmCTestTestHandler.h b/Source/CTest/cmCTestTestHandler.h
index 1b42647..f2da320 100644
--- a/Source/CTest/cmCTestTestHandler.h
+++ b/Source/CTest/cmCTestTestHandler.h
@@ -151,6 +151,7 @@ public:
     // return code of test which will mark test as "not run"
     int SkipReturnCode;
     std::vector<std::string> Environment;
+    std::vector<std::string> EnvironmentModification;
     std::vector<std::string> Labels;
     std::set<std::string> LockedResources;
     std::set<std::string> FixturesSetup;
diff --git a/Tests/Environment/CMakeLists.txt b/Tests/Environment/CMakeLists.txt
index 2b18d24..17009bd 100644
--- a/Tests/Environment/CMakeLists.txt
+++ b/Tests/Environment/CMakeLists.txt
@@ -9,6 +9,7 @@ add_test(Environment1 Environment)
 add_test(Environment2 Environment)
 add_test(EchoEnvironment1 ${CMAKE_COMMAND} -E environment)
 add_test(EchoEnvironment2 ${CMAKE_COMMAND} -E environment)
+add_test(EchoEnvironment3 ${CMAKE_COMMAND} -P "${CMAKE_CURRENT_SOURCE_DIR}/check_mod.cmake")
 
 # Make sure "CMAKE_ENV.*Happy Thanksgiving" is in the output of
 # the "1" tests:
@@ -24,3 +25,37 @@ set_tests_properties(Environment1 EchoEnvironment1 PROPERTIES
 set_tests_properties(Environment2 EchoEnvironment2 PROPERTIES
   FAIL_REGULAR_EXPRESSION "CMAKE_ENV.*Happy Thanksgiving"
 )
+
+set_property(TEST EchoEnvironment3
+  PROPERTY ENVIRONMENT_MODIFICATION
+    # Variables expected to be unset.
+    "UNSET_EXPLICIT=set:value"
+    "UNSET_EXPLICIT=unset:"
+    "UNSET_VIA_RESET=set:value"
+    "UNSET_VIA_RESET=reset:"
+
+    # Direct settings.
+    "DIRECT=set:old"
+    "DIRECT=set:new"
+
+    # String manipulation.
+    "STRING_MANIP=set:-core-"
+    "STRING_MANIP=string_append:post-"
+    "STRING_MANIP=string_prepend:-pre"
+    "STRING_MANIP=string_append:suffix"
+    "STRING_MANIP=string_prepend:prefix"
+
+    # Path manipulation.
+    "PATH_MANIP=set:core"
+    "PATH_MANIP=path_list_append:post"
+    "PATH_MANIP=path_list_prepend:pre"
+    "PATH_MANIP=path_list_append:suffix"
+    "PATH_MANIP=path_list_prepend:prefix"
+
+    # CMake list manipulation.
+    "CMAKE_LIST_MANIP=set:core"
+    "CMAKE_LIST_MANIP=cmake_list_append:post"
+    "CMAKE_LIST_MANIP=cmake_list_prepend:pre"
+    "CMAKE_LIST_MANIP=cmake_list_append:suffix"
+    "CMAKE_LIST_MANIP=cmake_list_prepend:prefix"
+)
diff --git a/Tests/Environment/check_mod.cmake b/Tests/Environment/check_mod.cmake
new file mode 100644
index 0000000..16d02f2
--- /dev/null
+++ b/Tests/Environment/check_mod.cmake
@@ -0,0 +1,55 @@
+execute_process(
+  COMMAND ${CMAKE_COMMAND} -E environment
+  OUTPUT_VARIABLE out
+  ERROR_VARIABLE err
+  RESULT_VARIABLE res)
+
+if (res)
+  message(FATAL_ERROR "Failed with exit code ${res}: ${err}")
+endif ()
+
+if (CMAKE_HOST_WIN32)
+  set(path_sep ";")
+else ()
+  set(path_sep ":")
+endif ()
+
+set(unexpect_UNSET_EXPLICIT "")
+set(unexpect_UNSET_VIA_RESET "")
+set(expect_DIRECT "new")
+set(expect_STRING_MANIP "prefix-pre-core-post-suffix")
+set(expect_PATH_MANIP "prefix${path_sep}pre${path_sep}core${path_sep}post${path_sep}suffix")
+set(expect_CMAKE_LIST_MANIP "prefix;pre;core;post;suffix")
+
+set(expected_vars
+  DIRECT
+  STRING_MANIP
+  PATH_MANIP
+  CMAKE_LIST_MANIP)
+
+while (out)
+  string(FIND "${out}" "\n" nl_pos)
+  string(SUBSTRING "${out}" 0 "${nl_pos}" line)
+  math(EXPR line_next "${nl_pos} + 1")
+  string(SUBSTRING "${out}" "${line_next}" -1 out)
+
+  string(FIND "${line}" "=" eq_pos)
+  string(SUBSTRING "${line}" 0 "${eq_pos}" name)
+  math(EXPR value_start "${eq_pos} + 1")
+  string(SUBSTRING "${line}" "${value_start}" -1 value)
+
+  if (DEFINED "unexpect_${name}")
+    message(SEND_ERROR "Found `${name}=${value}` when it should have been unset")
+  elseif (DEFINED "expect_${name}")
+    list(REMOVE_ITEM expected_vars "${name}")
+    if (expect_${name} STREQUAL value)
+      message(STATUS "Found `${name}=${value}` as expected")
+    else ()
+      message(SEND_ERROR "Found `${name}=${value}` when it should have been ${expect_${name}}")
+    endif ()
+  endif ()
+endwhile ()
+
+if (expected_vars)
+  message(SEND_ERROR "Did not test expected variables: ${expected_vars}")
+endif ()
diff --git a/Tests/RunCMake/CMakeLists.txt b/Tests/RunCMake/CMakeLists.txt
index 59fa9dc..5e0fefd 100644
--- a/Tests/RunCMake/CMakeLists.txt
+++ b/Tests/RunCMake/CMakeLists.txt
@@ -374,6 +374,7 @@ add_RunCMake_test(ctest_disabled_test)
 add_RunCMake_test(ctest_skipped_test)
 add_RunCMake_test(ctest_update)
 add_RunCMake_test(ctest_upload)
+add_RunCMake_test(ctest_environment)
 add_RunCMake_test(ctest_fixtures)
 add_RunCMake_test(file -DMSYS=${MSYS})
 add_RunCMake_test(file-CHMOD -DMSYS=${MSYS})
diff --git a/Tests/RunCMake/ctest_environment/CMakeLists.txt.in b/Tests/RunCMake/ctest_environment/CMakeLists.txt.in
new file mode 100644
index 0000000..c9c4a64
--- /dev/null
+++ b/Tests/RunCMake/ctest_environment/CMakeLists.txt.in
@@ -0,0 +1,3 @@
+cmake_minimum_required(VERSION 3.21.0)
+project("@CASE_NAME@" NONE)
+include("@CASE_SOURCE_DIR@/@CASE_NAME@.cmake")
diff --git a/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-invalid-op-result.txt b/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-invalid-op-result.txt
new file mode 100644
index 0000000..b57e2de
--- /dev/null
+++ b/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-invalid-op-result.txt
@@ -0,0 +1 @@
+(-1|255)
diff --git a/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-invalid-op-stderr.txt b/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-invalid-op-stderr.txt
new file mode 100644
index 0000000..5b56d6f
--- /dev/null
+++ b/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-invalid-op-stderr.txt
@@ -0,0 +1 @@
+Error: Unrecognized environment manipulation argument: unknown
diff --git a/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-invalid-op.cmake b/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-invalid-op.cmake
new file mode 100644
index 0000000..d6ca4b2
--- /dev/null
+++ b/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-invalid-op.cmake
@@ -0,0 +1,6 @@
+include(CTest)
+add_test(NAME cmake_version COMMAND "${CMAKE_COMMAND}" --version)
+
+set_property(TEST cmake_version
+  PROPERTY ENVIRONMENT_MODIFICATION
+    INVALID_OP=unknown:)
diff --git a/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-no-colon-result.txt b/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-no-colon-result.txt
new file mode 100644
index 0000000..b57e2de
--- /dev/null
+++ b/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-no-colon-result.txt
@@ -0,0 +1 @@
+(-1|255)
diff --git a/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-no-colon-stderr.txt b/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-no-colon-stderr.txt
new file mode 100644
index 0000000..3ba6ba7
--- /dev/null
+++ b/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-no-colon-stderr.txt
@@ -0,0 +1 @@
+Error: Missing `:` after the operation in: MISSING_COLON=unset
diff --git a/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-no-colon.cmake b/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-no-colon.cmake
new file mode 100644
index 0000000..601dd8b
--- /dev/null
+++ b/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-no-colon.cmake
@@ -0,0 +1,6 @@
+include(CTest)
+
+add_test(NAME cmake_version COMMAND "${CMAKE_COMMAND}" --version)
+set_property(TEST cmake_version
+  PROPERTY ENVIRONMENT_MODIFICATION
+    MISSING_COLON=unset)
diff --git a/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-no-equals-result.txt b/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-no-equals-result.txt
new file mode 100644
index 0000000..b57e2de
--- /dev/null
+++ b/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-no-equals-result.txt
@@ -0,0 +1 @@
+(-1|255)
diff --git a/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-no-equals-stderr.txt b/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-no-equals-stderr.txt
new file mode 100644
index 0000000..20bc9a5
--- /dev/null
+++ b/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-no-equals-stderr.txt
@@ -0,0 +1 @@
+Error: Missing `=` after the variable name in: MISSING_EQUAL
diff --git a/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-no-equals.cmake b/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-no-equals.cmake
new file mode 100644
index 0000000..18448cf
--- /dev/null
+++ b/Tests/RunCMake/ctest_environment/ENVIRONMENT_MODIFICATION-no-equals.cmake
@@ -0,0 +1,6 @@
+include(CTest)
+
+add_test(NAME cmake_version COMMAND "${CMAKE_COMMAND}" --version)
+set_property(TEST cmake_version
+  PROPERTY ENVIRONMENT_MODIFICATION
+    MISSING_EQUAL)
diff --git a/Tests/RunCMake/ctest_environment/RunCMakeTest.cmake b/Tests/RunCMake/ctest_environment/RunCMakeTest.cmake
new file mode 100644
index 0000000..3447779
--- /dev/null
+++ b/Tests/RunCMake/ctest_environment/RunCMakeTest.cmake
@@ -0,0 +1,12 @@
+include(RunCTest)
+
+# Isolate our ctest runs from external environment.
+unset(ENV{CTEST_PARALLEL_LEVEL})
+unset(ENV{CTEST_OUTPUT_ON_FAILURE})
+
+set(CASE_SOURCE_DIR "${RunCMake_SOURCE_DIR}")
+set(RunCTest_VERBOSE_FLAG "-VV")
+
+run_ctest(ENVIRONMENT_MODIFICATION-invalid-op)
+run_ctest(ENVIRONMENT_MODIFICATION-no-colon)
+run_ctest(ENVIRONMENT_MODIFICATION-no-equals)
diff --git a/Tests/RunCMake/ctest_environment/test.cmake.in b/Tests/RunCMake/ctest_environment/test.cmake.in
new file mode 100644
index 0000000..ca23c83
--- /dev/null
+++ b/Tests/RunCMake/ctest_environment/test.cmake.in
@@ -0,0 +1,16 @@
+cmake_minimum_required(VERSION 3.7)
+
+set(CTEST_SITE                          "test-site")
+set(CTEST_BUILD_NAME                    "test-build-name")
+set(CTEST_SOURCE_DIRECTORY              "@RunCMake_BINARY_DIR@/@CASE_NAME@")
+set(CTEST_BINARY_DIRECTORY              "@RunCMake_BINARY_DIR@/@CASE_NAME@-build")
+set(CTEST_CMAKE_GENERATOR               "@RunCMake_GENERATOR@")
+set(CTEST_CMAKE_GENERATOR_PLATFORM      "@RunCMake_GENERATOR_PLATFORM@")
+set(CTEST_CMAKE_GENERATOR_TOOLSET       "@RunCMake_GENERATOR_TOOLSET@")
+set(CTEST_BUILD_CONFIGURATION           "$ENV{CMAKE_CONFIG_TYPE}")
+
+set(ctest_test_args "@CASE_CTEST_TEST_ARGS@")
+ctest_start(Experimental)
+ctest_configure()
+ctest_build()
+ctest_test(${ctest_test_args})