tests: skip gmock test if gtest or gmock not installed

test cases/frameworks/3 gmock/meson.build

@@ -3,8 +3,14 @@ project('gmock test', 'cpp')
 # Using gmock without gtest is a pain so just
 # don't support that then.
 
-gtest = dependency('gtest', main : true)
-gmock = dependency('gmock')
+gtest = dependency('gtest', main : true, required : false)
+if not gtest.found()
+  error('MESON_SKIP_TEST: gtest not installed.')
+endif
+gmock = dependency('gmock', required : false)
+if not gmock.found()
+  error('MESON_SKIP_TEST: gmock not installed.')
+endif
 
 e = executable('gmocktest', 'gmocktest.cc', dependencies : [gtest, gmock])
 test('gmock test', e)