Fix array of strings being incorrectly converted to object when used with property matcher in snapshot.

Author: scotthovestadt

e2e/__tests__/__snapshots__/snapshotSerializers.test.ts.snap

@@ -2,6 +2,13 @@
 
 exports[`Snapshot serializers renders snapshot 1`] = `
 Object {
+  "snapshot serializers works with array of strings in property matcher 1": "
+Object {
+  \\"arrayOfStrings\\": Array [
+    \\"stream\\",
+  ],
+}
+",
   "snapshot serializers works with default serializers 1": "
 <div
   id=\\"foo\\"

e2e/__tests__/snapshotSerializers.test.ts

@@ -20,8 +20,8 @@ const runAndAssert = () => {
     '--no-cache',
   ]);
   const json = result.json;
-  expect(json.numTotalTests).toBe(7);
-  expect(json.numPassedTests).toBe(7);
+  expect(json.numTotalTests).toBe(8);
+  expect(json.numPassedTests).toBe(8);
   expect(json.numFailedTests).toBe(0);
   expect(json.numPendingTests).toBe(0);
   expect(result.status).toBe(0);

e2e/snapshot-serializers/__tests__/snapshot.test.js

@@ -91,4 +91,12 @@ describe('snapshot serializers', () => {
     });
     expect(test).toMatchSnapshot();
   });
+
+  it('works with array of strings in property matcher', () => {
+    expect({
+      arrayOfStrings: ['stream'],
+    }).toMatchSnapshot({
+      arrayOfStrings: ['stream'],
+    });
+  });
 });

packages/jest-snapshot/src/utils.ts

@@ -194,8 +194,8 @@ const deepMergeArray = (target: Array<any>, source: Array<any>) => {
 };
 
 export const deepMerge = (target: any, source: any) => {
-  const mergedOutput = {...target};
   if (isObject(target) && isObject(source)) {
+    const mergedOutput = {...target};
     Object.keys(source).forEach(key => {
       if (isObject(source[key]) && !source[key].$$typeof) {
         if (!(key in target)) Object.assign(mergedOutput, {[key]: source[key]});
@@ -206,6 +206,8 @@ export const deepMerge = (target: any, source: any) => {
         Object.assign(mergedOutput, {[key]: source[key]});
       }
     });
+    return mergedOutput;
+  } else {
+    return target;
   }
-  return mergedOutput;
 };