Support printing sensors using ign model (#1157)

* Support printing sensors using Print information about models.

  ign model [options]

Available Options:
  --list                     Get a list of the available models.
  -m [--model] arg           Select the model to be shown.
  -p [--pose]                Print the pose of the model.
  -l [--link]  arg           Select a link to show its properties.
                             If no arg is passed all links are printed
                             Requires the -m option

                             E.g. to get information about the
                             caster link in the diff_drive world, run:
                             ign model -m vehicle_blue -l caster

  -s [--sensor]  arg         Select a sensor to show its properties.
                             If no arg is passed all sensors are printed
                             Requires the -m and -l options

                             E.g. to get information about the
                             imu sensor in the sensors world, run:
                             ign model -m sensors_box -l link -s imu

  -j [--joint] arg           Select a joint to show its properties.
                             If no arg is passed all joints are printed
                             Requires the -m option

                             E.g. to get information about the
                             caster_wheel joint in the diff_drive
                             world, run:
                             ign model -m vehicle_blue -j caster_wheel

  -h [--help]                Print this help message.

  --force-version <VERSION>  Use a specific library version.

  --versions                 Show the available versions.

Signed-off-by: Nate Koenig <nate@openrobotics.org>

* Added tests

Signed-off-by: Nate Koenig <nate@openrobotics.org>

* Update documentation

Signed-off-by: Nate Koenig <nate@openrobotics.org>

* use joinPaths

Signed-off-by: Nate Koenig <nate@openrobotics.org>

* Use commas

Signed-off-by: Nate Koenig <nate@openrobotics.org>

* More commas

Signed-off-by: Nate Koenig <nate@openrobotics.org>

* Moved test to require DRI

Signed-off-by: Nate Koenig <nate@openrobotics.org>

Co-authored-by: Nate Koenig <nate@openrobotics.org>

CMakeLists.txt

@@ -34,6 +34,9 @@ else()
   set (EXTRA_TEST_LIB_DEPS)
 endif()
 
+include(test/find_dri.cmake)
+FindDRI()
+
 #============================================================================
 # Search for project-specific dependencies
 #============================================================================

src/CMakeLists.txt

@@ -78,7 +78,6 @@ set (gtest_sources
   EventManager_TEST.cc
   Link_TEST.cc
   Model_TEST.cc
-  ModelCommandAPI_TEST.cc
   SdfEntityCreator_TEST.cc
   SdfGenerator_TEST.cc
   ServerConfig_TEST.cc
@@ -95,6 +94,24 @@ set (gtest_sources
   network/NetworkManager_TEST.cc
 )
 
+# Tests that require a valid display
+set(tests_needing_display
+  ModelCommandAPI_TEST.cc
+)
+
+# Add systems that need a valid display here.
+# \todo(anyone) Find a way to run these tests with a virtual display such Xvfb
+# or Xdummy instead of skipping them
+if(VALID_DISPLAY AND VALID_DRI_DISPLAY)
+  list(APPEND gtest_sources ${tests_needing_display})
+else()
+  message(STATUS
+    "Skipping these UNIT tests because a valid display was not found:")
+  foreach(test ${tests_needing_display})
+    message(STATUS " ${test}")
+  endforeach(test)
+endif()
+
 if (MSVC)
   # Warning #4251 is the "dll-interface" warning that tells you when types used
   # by a class are not being exported. These generated source files have private