Fix -Wuninitialized-const-reference (#485)

(cherry picked from commit 42d3050)

Author: christophfroehlich

control_toolbox/test/control_filters/test_exponential_filter.cpp

@@ -23,7 +23,7 @@ TEST_F(FilterTest, TestExponentialFilterThrowsUnconfigured)
 {
   std::shared_ptr<filters::FilterBase<double>> filter_ =
     std::make_shared<control_filters::ExponentialFilter<double>>();
-  double in, out;
+  double in = 42., out;
   ASSERT_THROW(filter_->update(in, out), std::runtime_error);
 }
 

control_toolbox/test/control_filters/test_low_pass_filter.cpp

@@ -73,7 +73,7 @@ TEST_F(FilterTest, TestLowPassFilterThrowsUnconfigured)
 {
   std::shared_ptr<filters::FilterBase<double>> filter_ =
     std::make_shared<control_filters::LowPassFilter<double>>();
-  double in, out;
+  double in = 42., out;
   ASSERT_THROW(filter_->update(in, out), std::runtime_error);
 }
 

control_toolbox/test/control_filters/test_rate_limiter.cpp

@@ -72,7 +72,7 @@ TEST_F(FilterTest, TestRateLimiterThrowsUnconfigured)
 {
   std::shared_ptr<filters::FilterBase<double>> filter_ =
     std::make_shared<control_filters::RateLimiter<double>>();
-  double in, out;
+  double in = 42., out;
   ASSERT_THROW(filter_->update(in, out), std::runtime_error);
 }