Added tests for MakeMakefile#test_egrep_cpp

test/mkmf/test_egrep_cpp.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: false
+require_relative 'base'
+require 'tempfile'
+
+class TestMkmf
+  class TestEgrepCpp < TestMkmf
+    def test_egrep_cpp
+      assert_equal(true, egrep_cpp(/ruby_init/, ""), MKMFLOG)
+    end
+
+    def test_not_have_func
+      assert_equal(false, egrep_cpp(/never match/, ""), MKMFLOG)
+    end
+  end
+end