[OTLP Exporter] Assert empty env vars in tests

Check that env variables were unset after test.

Author: ozerovandrei

opentelemetry-otlp/src/lib.rs

@@ -407,6 +407,8 @@ mod tests {
 
         std::env::remove_var(OTEL_EXPORTER_OTLP_ENDPOINT);
         std::env::remove_var(OTEL_EXPORTER_OTLP_TIMEOUT);
+        assert!(std::env::var(OTEL_EXPORTER_OTLP_ENDPOINT).is_err());
+        assert!(std::env::var(OTEL_EXPORTER_OTLP_TIMEOUT).is_err());
     }
 
     #[test]
@@ -433,5 +435,7 @@ mod tests {
 
         std::env::remove_var(OTEL_EXPORTER_OTLP_TRACES_ENDPOINT);
         std::env::remove_var(OTEL_EXPORTER_OTLP_TRACES_TIMEOUT);
+        assert!(std::env::var(OTEL_EXPORTER_OTLP_TRACES_ENDPOINT).is_err());
+        assert!(std::env::var(OTEL_EXPORTER_OTLP_TRACES_TIMEOUT).is_err());
     }
 }