Add type assertion for sample_rate

lib/statsd/instrument/assertions.rb

@@ -42,6 +42,7 @@ def assert_statsd_call(metric_type, metric_name, options = {}, &block)
 
     metrics.each do |metric|
 
+      assert within_numeric_range?(metric.sample_rate), "Unexpected sample rate type for metric #{metric_name}, must be numeric"
       assert_equal options[:sample_rate], metric.sample_rate, "Unexpected StatsD sample rate for metric #{metric_name}" if options[:sample_rate]
       assert_equal options[:value], metric.value, "Unexpected value submitted for StatsD metric #{metric_name}" if options[:value]
 
@@ -66,4 +67,8 @@ def assert_statsd_call(metric_type, metric_name, options = {}, &block)
       metric
     end
   end
+
+  def within_numeric_range?(object)
+    object.kind_of?(Numeric) && (0.0..1.0).cover?(object)
+  end
 end

test/assertions_test.rb

@@ -163,6 +163,14 @@ def test_assert_statsd_call_with_tags
     end
   end
 
+  def test_assert_statsd_call_with_wrong_sample_rate_type
+    assert_assertion_triggered "Unexpected sample rate type for metric counter, must be numeric" do
+      @test_case.assert_statsd_increment('counter', tags: ['a', 'b']) do
+        StatsD.increment('counter', sample_rate: 'abc', tags:  ['a', 'b'])
+      end
+    end
+  end
+
   def test_nested_assertions
     assert_no_assertion_triggered do
       @test_case.assert_statsd_increment('counter1') do