share in-memory exporter between test cases

instead of creating a new exporter in RumRailsTest and
RackRailsTest have EXPORTER instance created globally
and reset it in the teardown method of the testcases.

It may be useful to figure out in the future why creating
a new exporter in each testcase was resulting in no spans
making it to the exporter in the second test to run.

test/splunk/instrumentation/rack_test.rb

@@ -11,11 +11,7 @@ module Splunk
   class RumRackTest < Test::Unit::TestCase
     include Rack::Test::Methods
 
-    EXPORTER = OpenTelemetry::SDK::Trace::Export::InMemorySpanExporter.new
-
     def setup
-      EXPORTER.reset
-
       with_env("OTEL_SERVICE_NAME" => "test-service") do
         span_processor = OpenTelemetry::SDK::Trace::Export::SimpleSpanProcessor.new(EXPORTER)
         Splunk::Otel.configure do |c|
@@ -26,7 +22,7 @@ def setup
     end
 
     def teardown
-      OpenTelemetry.tracer_provider.shutdown
+      reset_opentelemetry
     end
 
     def app

test/splunk/instrumentation/rails_test.rb

@@ -17,11 +17,7 @@ module Splunk
   class RumRailsTest < Test::Unit::TestCase
     include Rack::Test::Methods
 
-    EXPORTER = OpenTelemetry::SDK::Trace::Export::InMemorySpanExporter.new
-
     def setup
-      EXPORTER.reset
-
       with_env("OTEL_SERVICE_NAME" => "test-service") do
         span_processor = OpenTelemetry::SDK::Trace::Export::SimpleSpanProcessor.new(EXPORTER)
         Splunk::Otel.configure do |c|
@@ -33,7 +29,7 @@ def setup
     end
 
     def teardown
-      OpenTelemetry.tracer_provider.shutdown
+      reset_opentelemetry
     end
 
     def app

test/test_helper.rb

@@ -8,6 +8,8 @@
 
 require "test-unit"
 
+EXPORTER = OpenTelemetry::SDK::Trace::Export::InMemorySpanExporter.new
+
 def with_env(new_env)
   env_to_reset = ENV.select { |k, _| new_env.key?(k) }
   keys_to_delete = new_env.keys - ENV.keys
@@ -17,3 +19,17 @@ def with_env(new_env)
   env_to_reset.each_pair { |k, v| ENV[k] = v }
   keys_to_delete.each { |k| ENV.delete(k) }
 end
+
+def reset_opentelemetry
+  EXPORTER.reset
+
+  OpenTelemetry.instance_variable_set(
+    :@tracer_provider,
+    OpenTelemetry::Internal::ProxyTracerProvider.new
+  )
+
+  # OpenTelemetry will load the defaults
+  # on the next call to any of these methods
+  OpenTelemetry.error_handler = nil
+  OpenTelemetry.propagation = nil
+end