diff --git a/org.hl7.fhir.r4/src/main/resources/snapshot-generation-tests.xml b/org.hl7.fhir.r4/src/main/resources/snapshot-generation-tests.xml
index ba13ea65e..d0f59ad8d 100644
--- a/org.hl7.fhir.r4/src/main/resources/snapshot-generation-tests.xml
+++ b/org.hl7.fhir.r4/src/main/resources/snapshot-generation-tests.xml
@@ -39,7 +39,7 @@
  34. Referencing a custom extension
  35. Referencing a profiled custom extension
  36. Deep recursion
- 37. Constrained polymorphic elements
+ 37. Test Bad Path
  38. Deep nesting
 -->
   <contained>
@@ -1832,10 +1832,10 @@
   <contained>
     <StructureDefinition>
       <id value="t37"/>
-      <url value="urn:uuid:2918bbbf-2145-4c13-822e-7dfd758694ec"/>
-      <name value="t38"/>
+      <url value="urn:uuid:44a92f3e-3681-4dbc-baa2-48a07e2765ca"/>
+      <name value="t37"/>
       <status value="draft"/>
-      <description value="fixture for #38: Constrained polymporphic elements"/>
+      <description value="fixture for #37: Test bad Path"/>
       <kind value="resource"/>
       <abstract value="false"/>
       <type value="MedicationDispense"/>
@@ -1846,10 +1846,9 @@
           <path value="MedicationDispense"/>
         </element>
         <element>
-          <path value="MedicationDispense.dosageInstruction"/>
+          <path value="MedicationDispense.invalid"/>
         </element>
         <element>
-          <!-- Including this element isn't strictly necessary to reproduce the problem.  However, its inclusion seemed to prevent certain errors from showing up when I trimmed the instance, so I'm leaving it in -->
           <path value="MedicationDispense.dosageInstruction.extension"/>
           <slicing>
             <discriminator>
@@ -1860,20 +1859,6 @@
           </slicing>
           <mustSupport value="true"/>
         </element>
-        <element>
-          <path value="MedicationOrder.dosageInstruction.additionalInstruction"/>
-          <type>
-            <code value="Quantity"/>
-          </type>
-          <mustSupport value="true"/>
-        </element>
-        <element>
-          <path value="MedicationOrder.dosageInstruction.doseQuantity"/>
-          <type>
-            <code value="Quantity"/>
-          </type>
-          <mustSupport value="true"/>
-        </element>
       </differential>
     </StructureDefinition>
   </contained>
@@ -2007,6 +1992,13 @@
         <sourceId value="t1"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test1-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test1-1"/>
@@ -2068,6 +2060,13 @@
         <sourceId value="t2"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test2-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test2-1"/>
@@ -2102,6 +2101,13 @@
         <sourceId value="t3"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test3-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test3-1"/>
@@ -2145,6 +2151,13 @@
         <sourceId value="t4"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test4-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test4-1"/>
@@ -2170,6 +2183,13 @@
         <sourceId value="t5"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test5-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test5-1"/>
@@ -2204,6 +2224,13 @@
         <sourceId value="t6"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test6-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test6-1"/>
@@ -2238,6 +2265,13 @@
         <sourceId value="t7"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test7-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test7-1"/>
@@ -2263,6 +2297,13 @@
         <sourceId value="t8"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test8-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test8-1"/>
@@ -2297,6 +2338,13 @@
         <sourceId value="t9"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test9-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test9-1"/>
@@ -2331,6 +2379,13 @@
         <sourceId value="t10"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test10-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test10-1"/>
@@ -2401,6 +2456,13 @@
         <sourceId value="t11"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test11-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test11-1"/>
@@ -2480,6 +2542,13 @@
         <sourceId value="t12"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test12-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test12-1"/>
@@ -2550,6 +2619,13 @@
         <sourceId value="t12a"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test12a-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test12a-1"/>
@@ -2611,6 +2687,13 @@
         <sourceId value="t13"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test13-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test13-1"/>
@@ -2819,6 +2902,13 @@
         <sourceId value="t14"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test14-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test14-1"/>
@@ -2843,6 +2933,13 @@
         <sourceId value="t15"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test15-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test15-1"/>
@@ -2867,6 +2964,13 @@
         <sourceId value="t16"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test16-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test16-1"/>
@@ -2891,6 +2995,13 @@
         <sourceId value="t17"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test17-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test17-1"/>
@@ -2970,6 +3081,13 @@
         <sourceId value="t18"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test18-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test18-1"/>
@@ -3049,6 +3167,13 @@
         <sourceId value="t19"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test19-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test19-1"/>
@@ -3110,6 +3235,13 @@
         <sourceId value="t20"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test20-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test20-1"/>
@@ -3180,6 +3312,13 @@
         <sourceId value="t21"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test21-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test21-1"/>
@@ -3241,6 +3380,13 @@
         <sourceId value="t22"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test22-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test22-1"/>
@@ -3266,6 +3412,13 @@
         <sourceId value="t23"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test23-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test23-1"/>
@@ -3302,6 +3455,13 @@
         <sourceId value="t24b"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test24-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test24-1"/>
@@ -3334,6 +3494,13 @@
         <sourceId value="t25b"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test25-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test25-1"/>
@@ -3359,6 +3526,13 @@
         <sourceId value="t26"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test26-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test26-1"/>
@@ -3383,6 +3557,13 @@
         <sourceId value="t27"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test27-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test27-1"/>
@@ -3418,6 +3599,13 @@
         <sourceId value="t28"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test28-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test28-1"/>
@@ -3444,6 +3632,13 @@
         <sourceId value="t29"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test29-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test29-1"/>
@@ -3481,7 +3676,14 @@
     </action>
     <action>
       <assert>
-        <label value="test30"/>
+        <label value="test30-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
+    <action>
+      <assert>
+        <label value="test30-1"/>
         <description value="Snapshot doesn't result in an error'"/>
         <direction value="response"/>
         <expression value="fixture('t30bo').snapshot.element.count().trace('t30bo')>1"/>
@@ -3505,6 +3707,13 @@
         <sourceId value="t31"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test31-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test31"/>
@@ -3531,6 +3740,13 @@
         <sourceId value="t32"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test32-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test32"/>
@@ -3557,6 +3773,13 @@
         <sourceId value="t33"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test33-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test33"/>
@@ -3583,6 +3806,13 @@
         <sourceId value="t34"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test34-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test34"/>
@@ -3618,6 +3848,13 @@
         <sourceId value="t35"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test35-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test35"/>
@@ -3653,6 +3890,13 @@
         <sourceId value="t36"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test36-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test36"/>
@@ -3665,7 +3909,7 @@
   </test>
   <test>
     <name value="Test37"/>
-    <description value="Test deep nesting"/>
+    <description value="Test bad path"/>
     <action>
       <operation>
         <type>
@@ -3681,11 +3925,9 @@
     </action>
     <action>
       <assert>
-        <label value="test37"/>
-        <description value="Snapshot includes polymorphic constrained element"/>
-        <direction value="response"/>
-        <expression value="fixture('t37o').snapshot.element.where(path = 'MedicationDispense.dosageInstruction.doseQuantity').count() = 1"/>
-        <warningOnly value="false"/>
+        <label value="test37-0"/>
+        <description value="Snapshot must not generate ok"/>
+        <response value="bad"/>
       </assert>
     </action>
   </test>
@@ -3705,6 +3947,13 @@
         <sourceId value="t38"/>
       </operation>
     </action>
+    <action>
+      <assert>
+        <label value="test38-0"/>
+        <description value="Snapshot must generate ok"/>
+        <response value="okay"/>
+      </assert>
+    </action>
     <action>
       <assert>
         <label value="test38"/>
diff --git a/org.hl7.fhir.r4/src/test/java/org/hl7/fhir/r4/test/SnapShotGenerationTests.java b/org.hl7.fhir.r4/src/test/java/org/hl7/fhir/r4/test/SnapShotGenerationTests.java
index 86952aa2c..d5edf7710 100644
--- a/org.hl7.fhir.r4/src/test/java/org/hl7/fhir/r4/test/SnapShotGenerationTests.java
+++ b/org.hl7.fhir.r4/src/test/java/org/hl7/fhir/r4/test/SnapShotGenerationTests.java
@@ -33,6 +33,7 @@ import org.hl7.fhir.r4.model.StructureDefinition;
 import org.hl7.fhir.r4.model.StructureDefinition.StructureDefinitionKind;
 import org.hl7.fhir.r4.model.StructureDefinition.TypeDerivationRule;
 import org.hl7.fhir.r4.model.TestScript;
+import org.hl7.fhir.r4.model.TestScript.AssertionResponseTypes;
 import org.hl7.fhir.r4.model.TestScript.SetupActionAssertComponent;
 import org.hl7.fhir.r4.model.TestScript.SetupActionOperationComponent;
 import org.hl7.fhir.r4.model.TestScript.TestActionComponent;
@@ -167,8 +168,8 @@ public class SnapShotGenerationTests {
               throw new Error("Unsupported: actions must have a label");
             if (!a.hasDescription())
               throw new Error("Unsupported: actions must have a description");
-            if (!a.hasExpression())
-              throw new Error("Unsupported: actions must have an expression");
+            if (!a.hasExpression() && !a.hasResponse())
+              throw new Error("Unsupported: actions must have an expression or a response");
           } else {
             throw new Error("Unsupported: Unrecognized action type");            
           }
@@ -323,33 +324,35 @@ public class SnapShotGenerationTests {
 
     resolveFixtures();
     
+    TestScript.AssertionResponseTypes lastOpOutcome = null;
     for (int i = 0; i < test.getAction().size(); i++) {
       TestActionComponent action = test.getAction().get(i);
       if (action.hasOperation()) {
-        SetupActionOperationComponent op = action.getOperation();
-        Coding opType = op.getType();
-        if (opType.getSystem().equals("http://hl7.org/fhir/testscript-operation-codes") && opType.getCode().equals("snapshot")) {
-          StructureDefinition source = (StructureDefinition) context.fetchFixture(op.getSourceId());
-          StructureDefinition base = getSD(source.getBaseDefinition()); 
-          StructureDefinition output = source.copy();
-          ProfileUtilities pu = new ProfileUtilities(TestingUtilities.context(), null, new TestPKP());
-          pu.setIds(source, false);
-          if ("sort=true".equals(op.getParams())) {
-            List<String> errors = new ArrayList<String>();
-            pu.sortDifferential(base, output, source.getName(), errors);
-            if (errors.size() > 0)
-              throw new FHIRException("Sort failed: "+errors.toString());
-          }
-          pu.generateSnapshot(base, output, source.getUrl(), source.getName());
-          debugSaveResource(output);
-          context.fixtures.put(op.getResponseId(), output);
-          context.snapshots.put(output.getUrl(), output);
-          
-          new XmlParser().setOutputStyle(OutputStyle.PRETTY).compose(new FileOutputStream(Utilities.path(System.getProperty("java.io.tmpdir"), op.getResponseId()+".xml")), output);
-          if (output.getDifferential().hasElement())
-            new NarrativeGenerator("", "http://hl7.org/fhir", TestingUtilities.context()).setPkp(new TestPKP()).generate(output, null);
-          new XmlParser().setOutputStyle(OutputStyle.PRETTY).compose(new FileOutputStream(Utilities.path(System.getProperty("java.io.tmpdir"), op.getResponseId()+"-d.xml")), output);
-          
+        lastOpOutcome = AssertionResponseTypes.OKAY;
+        try {
+          SetupActionOperationComponent op = action.getOperation();
+          Coding opType = op.getType();
+          if (opType.getSystem().equals("http://hl7.org/fhir/testscript-operation-codes") && opType.getCode().equals("snapshot")) {
+            StructureDefinition source = (StructureDefinition) context.fetchFixture(op.getSourceId());
+            StructureDefinition base = getSD(source.getBaseDefinition()); 
+            StructureDefinition output = source.copy();
+            ProfileUtilities pu = new ProfileUtilities(TestingUtilities.context(), null, new TestPKP());
+            pu.setIds(source, false);
+            if ("sort=true".equals(op.getParams())) {
+              List<String> errors = new ArrayList<String>();
+              pu.sortDifferential(base, output, source.getName(), errors);
+              if (errors.size() > 0)
+                throw new FHIRException("Sort failed: "+errors.toString());
+            }
+            pu.generateSnapshot(base, output, source.getUrl(), source.getName());
+            debugSaveResource(output);
+            context.fixtures.put(op.getResponseId(), output);
+            context.snapshots.put(output.getUrl(), output);
+            
+            new XmlParser().setOutputStyle(OutputStyle.PRETTY).compose(new FileOutputStream(Utilities.path(System.getProperty("java.io.tmpdir"), op.getResponseId()+".xml")), output);
+            if (output.getDifferential().hasElement())
+              new NarrativeGenerator("", "http://hl7.org/fhir", TestingUtilities.context()).setPkp(new TestPKP()).generate(output, null);
+            new XmlParser().setOutputStyle(OutputStyle.PRETTY).compose(new FileOutputStream(Utilities.path(System.getProperty("java.io.tmpdir"), op.getResponseId()+"-d.xml")), output);
         } else if (opType.getSystem().equals("http://hl7.org/fhir/testscript-operation-codes") && opType.getCode().equals("sortDifferential")) {
           StructureDefinition source = (StructureDefinition) context.fetchFixture(op.getSourceId());
           StructureDefinition base = getSD(source.getBaseDefinition()); 
@@ -368,10 +371,19 @@ public class SnapShotGenerationTests {
         } else {
           throw new Error("Unsupported operation: " + opType.getSystem() + " : " + opType.getCode());
         }
+        } catch (Exception e) {
+          lastOpOutcome = AssertionResponseTypes.BAD;
+        }
+        
       } else if (action.hasAssert()) {
         SetupActionAssertComponent a = action.getAssert();
-        boolean ok = fp.evaluateToBoolean(new StructureDefinition(), new StructureDefinition(), a.getExpression());
-        Assert.assertTrue(a.getLabel()+": "+a.getDescription(), ok);
+        if (a.getResponse() != null) {
+          Assert.assertTrue(a.getLabel()+" (response): "+a.getDescription(), a.getResponse() == lastOpOutcome);         
+        }
+        if (a.hasExpression()) {
+          boolean ok = fp.evaluateToBoolean(new StructureDefinition(), new StructureDefinition(), a.getExpression());
+          Assert.assertTrue(a.getLabel()+": "+a.getDescription(), ok);
+        }
       }
     }
     } catch (Exception e) {