Move SPM segment to the last order group within HL7 message (#9363)

Author: mpbrown

backend/src/main/java/gov/cdc/usds/simplereport/api/converter/HL7Converter.java

@@ -251,9 +251,9 @@ public ORU_R01 createLabReportMessage(
       // in a message as long as each specimen is associated with only one observation request (aka
       // test ordered LOINC). With how the app currently works, we will only ever have one specimen
       // in the entire HL7 message. That is only due to how the app is currently designed, not a
-      // constraint of HL7.
+      // constraint of HL7. This SPM segment should be attached to the last order group.
       // See page 83, HL7 v2.5.1 IG
-      if (orderObservationIndex == 0) {
+      if (orderObservationIndex == testOrderLoincToTestDetailsMap.size() - 1) {
         SPM specimen = orderGroup.getSPECIMEN().getSPM();
         populateSpecimen(specimen, 1, specimenId, specimenInput);
       }

backend/src/test/java/gov/cdc/usds/simplereport/api/converter/HL7ConverterTest.java

@@ -223,6 +223,10 @@ void createLabReportMessage_fromTestEvent_multiplex_onDeviceWithNoMultiplexTestO
     Parser parser = hapiContext.getPipeParser();
     String encodedMessage = parser.encode(message);
     assertThat(StringUtils.countMatches(encodedMessage, "OBR|")).isEqualTo(2);
+
+    assertThat(StringUtils.countMatches(encodedMessage, "SPM|")).isEqualTo(1);
+    String[] lines = encodedMessage.replace("\r", "\n").split("\n");
+    assertThat(lines[lines.length - 1]).contains("SPM|");
   }
 
   @Test