fix: incorrect evaluation details code returned for TYPE_MISMATCH (#117)

Author: greghuels

src/client/eppo-client-assignment-details.spec.ts

@@ -235,6 +235,49 @@ describe('EppoClient get*AssignmentDetails', () => {
     } as IAssignmentDetails<number>);
   });
 
+  it('should handle type mismatches with graceful failure mode enabled', () => {
+    const client = new EppoClient(storage);
+    client.setIsGracefulFailureMode(true);
+    const result = client.getBooleanAssignmentDetails('integer-flag', 'alice', {}, true);
+    expect(result).toEqual({
+      variation: true,
+      action: null,
+      evaluationDetails: {
+        environmentName: 'Test',
+        flagEvaluationCode: 'TYPE_MISMATCH',
+        flagEvaluationDescription:
+          'Variation value does not have the correct type. Found INTEGER, but expected BOOLEAN for flag integer-flag',
+        variationKey: null,
+        variationValue: null,
+        banditKey: null,
+        banditAction: null,
+        configFetchedAt: expect.any(String),
+        configPublishedAt: expect.any(String),
+        matchedRule: null,
+        matchedAllocation: null,
+        unmatchedAllocations: [],
+        unevaluatedAllocations: [
+          {
+            key: 'targeted allocation',
+            allocationEvaluationCode: AllocationEvaluationCode.UNEVALUATED,
+            orderPosition: 1,
+          },
+          {
+            key: '50/50 split',
+            allocationEvaluationCode: AllocationEvaluationCode.UNEVALUATED,
+            orderPosition: 2,
+          },
+        ],
+      },
+    } as IAssignmentDetails<boolean>);
+  });
+
+  it('should throw an error for type mismatches with graceful failure mode disabled', () => {
+    const client = new EppoClient(storage);
+    client.setIsGracefulFailureMode(false);
+    expect(() => client.getBooleanAssignmentDetails('integer-flag', 'alice', {}, true)).toThrow();
+  });
+
   describe('UFC General Test Cases', () => {
     const testStart = Date.now();
 

src/client/eppo-client.ts

@@ -750,9 +750,15 @@ export default class EppoClient {
     }
 
     if (!checkTypeMatch(expectedVariationType, flag.variationType)) {
-      throw new TypeError(
-        `Variation value does not have the correct type. Found: ${flag.variationType} != ${expectedVariationType} for flag ${flagKey}`,
-      );
+      const errorMessage = `Variation value does not have the correct type. Found ${flag.variationType}, but expected ${expectedVariationType} for flag ${flagKey}`;
+      if (this.isGracefulFailureMode) {
+        const flagEvaluationDetails = flagEvaluationDetailsBuilder.buildForNoneResult(
+          'TYPE_MISMATCH',
+          errorMessage,
+        );
+        return noneResult(flagKey, subjectKey, subjectAttributes, flagEvaluationDetails);
+      }
+      throw new TypeError(errorMessage);
     }
 
     if (!flag.enabled) {
@@ -780,9 +786,9 @@ export default class EppoClient {
 
     if (result?.variation && !checkValueTypeMatch(expectedVariationType, result.variation.value)) {
       const { key: vKey, value: vValue } = result.variation;
-      const reason = `Expected variation type ${expectedVariationType} does not match for variation '${vKey}' with value ${vValue}`;
+      const reason = `Variation (${vKey}) is configured for type ${expectedVariationType}, but is set to incompatible value (${vValue})`;
       const flagEvaluationDetails = flagEvaluationDetailsBuilder.buildForNoneResult(
-        'TYPE_MISMATCH',
+        'ASSIGNMENT_ERROR',
         reason,
       );
       return noneResult(flagKey, subjectKey, subjectAttributes, flagEvaluationDetails);