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Added TASK.md to the chat.
Added package.json to the chat.
Added src\contacts.js to the chat.
Added src\test.js to the chat.
Added verify.js to the chat.


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► **THINKING**

Okay, let's see. The user wants me to complete the fixture task by implementing
the mergeDuplicates function. The main goal is to have the verify.js pass all
tests.

First, I need to check what's missing. The TASK.md says to implement
mergeDuplicates() that merges contacts with the same email, keeping the most
complete record. The existing tests in verify.js check for the function's
existence, exports, and specific test cases.

Looking at the current files, the contacts.js file doesn't have the
mergeDuplicates function yet. The verify.js tests are failing because
mergeDuplicates isn't implemented. The test.js file has a TODO for
mergeDuplicates tests, but the actual implementation is missing.

So, the first step is to add the mergeDuplicates function to contacts.js. The
function should take an array of contacts and merge duplicates based on email.
The merge should prioritize non-empty fields from the later contact in the
array (since "newer" means later in the input).

Let me think about how to structure mergeDuplicates. For each email, collect
all contacts with that email. Then, for each group, merge them by taking the
first non-null value for each field. Wait, but the task says "non-empty fields
from the newer record take priority; for this fixture, 'newer' means later in
the input array". So, when merging, if two contacts have the same email, the
one that appears later in the array should have its fields take precedence.

Wait, the example in verify.js test 'mergeDuplicates handles basic merge'
shows:

contacts = [
  createContact('Alice', 'alice@test.com', '555', 'Acme'),
  createContact('Alice Johnson', 'alice@test.com', null, null),
]

merged should have name 'Alice Johnson', phone '555', company 'Acme'? Wait, no.
Wait, the second contact has name 'Alice Johnson', email same, phone null,
company null. The first contact has name 'Alice', phone '555', company 'Acme'.
The merged should take the newer (second) contact's name, but phone and company
from the first? Wait, the test says:

"mergeDuplicates handles basic merge" test expects merged[0].email to be
'alice@test.com', and the merged array length 1. The test checks that the
merged contact has the name from the second contact (since it's newer), but
phone and company from the first? Wait, the test code says:

const contacts = [
  createContact('Alice', 'alice@test.com', '555', 'Acme'),
  createContact('Alice Johnson', 'alice@test.com', null, null),
];
const merged = mergeDuplicates(contacts);
if (merged.length !== 1) throw new Error(...);
if (merged[0].email !== 'alice@test.com') throw new Error(...);

So the merged contact should have email 'alice@test.com', which it does. But
the test doesn't check other fields. The next test, 'mergeDuplicates keeps most
complete data', checks that name and phone are preserved.

Wait, the second test:

contacts = [
  createContact(null, 'alice@test.com', '555', null),
  createContact('Alice', 'alice@test.com', null, 'Acme'),
];
merged should have name 'Alice', phone '555', company 'Acme'.

So, for each field, if the later contact (second one here) has a non-null
value, it takes precedence. Wait, the second contact has name 'Alice', phone
null, company 'Acme'. The first has name null, phone '555', company null. So
merged should have name 'Alice' (from second), phone '555' (from first),
company 'Acme' (from second). Wait, but the test says "non-empty fields from
the newer record take priority". Wait, newer means later in the array. So the
second contact is newer. So for each field, if the newer contact has a
non-empty value, use that; otherwise, use the older one.

Wait, the test says "non-empty fields from the newer record take priority". So
for each field, if the newer contact (later in array) has a non-empty value,
use that. Otherwise, use the older contact's value.

So for the second test case:

First contact: name null, phone '555', company null.

Second contact: name 'Alice', phone null, company 'Acme'.

Merged should have name 'Alice' (from newer), phone '555' (from older, since
newer has null), company 'Acme' (from newer).

Yes, that's what the test checks.

So the mergeDuplicates function should:

- Group contacts by email.

- For each group, merge the contacts into one, taking for each field the value
from the last contact in the group (since later in the array is newer).

Wait, but the group is all contacts with the same email. The order in the array
is preserved, so the last contact in the group (i.e., the one that appears
latest in the original array) should have its non-null fields take precedence.

Wait, but the test says "newer" means later in the input array. So for a group
of contacts with the same email, the one that comes later in the original array
is newer, so its fields should take precedence.

So, for each email group, we can iterate through the contacts in the group (in
the order they appear in the array), and for each field, if the current
contact's field is not null/empty, take it. Wait, but the merging should take
the latest non-null value. Wait, no: the newer contact (later in array) should
have its fields take precedence. So for each field, if the newer contact has a
value, use that; otherwise, use the older one.

Wait, for example, if contact A (older) has name 'Alice', contact B (newer) has
name 'Bob', then merged name should be 'Bob'.

So, for each field, the latest non-null value in the group (from the latest
contact) should be taken.

So, to merge a group, we can start with the first contact in the group, then
for each subsequent contact in the group, if a field is not null in the newer
contact, overwrite the merged field with that value.

Wait, but the group is in the order of the original array. So for a group
[contact1, contact2, contact3], contact3 is the newest. So when merging,
contact3's fields should take precedence over contact2's, which take precedence
over contact1's.

So, the merging process for a group would be:

- Start with the first contact in the group.

- For each subsequent contact in the group (from second to last), for each
field, if the field is not null in the current contact, set the merged field to
that value.

Wait, but the test says "non-empty fields from the newer record take priority".
So for each field, if the newer contact (later in array) has a non-empty value,
use that; otherwise, use the older one.

So, for each field, the latest non-null value in the group.

So, for a group, we can iterate through the contacts in the order they appear
(oldest to newest), and for each field, if the current contact's field is not
null, update the merged contact's field.

Wait, but the latest contact is the newest, so we want to take the latest
non-null value. So, for each field, the last non-null value in the group.

So, for example, if group has:

contact1: name 'Alice', phone null

contact2: name null, phone '555'

contact3: name 'Bob', phone null

Then merged name should be 'Bob' (from contact3), phone '555' (from contact2).

So, to merge, we can process the group from first to last, and for each field,
take the last non-null value.

So, the algorithm for merging a group:

- Initialize mergedContact as a copy of the first contact.

- For each subsequent contact in the group (from second to last):

   - For each field (name, email, phone, company), if the field is not null in
the current contact, set mergedContact[field] to that value.

Wait, but email is the key, so it's the same for all in the group. So email can
be ignored.

Wait, the email is the same for all in the group, so we don't need to merge
email.

So, for each group, we'll merge name, phone, company.

So, the function mergeDuplicates(contacts) should:

- Create a map where key is email, value is array of contacts with that email.

- For each email, merge the array of contacts into one contact.

- The merged contact should have the email (same as key), and for each field,
the latest non-null value from the contacts in the array.

- Then, return the array of merged contacts (one per email).

Wait, but the test cases expect that after merging, there are no duplicate
emails. So each merged contact has a unique email.

So, the steps:

1. Group contacts by email.

2. For each group, merge the contacts into a single contact, taking the latest
non-null values for each field.

3. Return the array of merged contacts.

Now, let's implement this in contacts.js.

The current contacts.js has createContact, findByEmail, addContact,
removeContact. We need to add mergeDuplicates.

So, in contacts.js, after the existing functions, add:

function mergeDuplicates(contacts) {
  const groups = new Map();
  for (const contact of contacts) {
    const email = contact.email;
    if (!email) continue; // Skip contacts without email
    if (!groups.has(email)) {
      groups.set(email, []);
    }
    groups.get(email).push(contact);
  }

  const merged = [];
  for (const [email, group] of groups) {
    let mergedContact = { email };
    // Start with the first contact in the group
    // But we need to merge all fields from the group, taking latest non-null
    // So iterate through the group in order (oldest to newest), and for each
field, take the latest non-null
    // So, for each field, the last non-null value in the group
    // Let's initialize mergedContact with the first contact's fields, then
update as we go through the group
    // But better to start with empty and accumulate the latest non-null
    // Wait, no. Let's process each contact in the group in order, and for each
field, if the current contact has a non-null value, set it.
    // So, for the group, we'll create a new contact, and for each contact in
the group (in order), if a field is not null, set it.
    // But since we want the latest non-null, processing in order (oldest to
newest) and taking the last non-null for each field is correct.

    // Initialize mergedContact with the first contact's fields, but maybe
better to start with nulls and then update.
    // Let's start with an empty object for mergedContact, then for each
contact in the group, merge its fields.
    // But since we want the latest non-null, we can iterate through the group
and for each field, if the current contact has a non-null value, set it.
    // So, let's create a temporary object for the merged contact.
    let mergedContact = { email };
    for (const contact of group) {
      if (contact.name !== null) mergedContact.name = contact.name;
      if (contact.phone !== null) mergedContact.phone = contact.phone;
      if (contact.company !== null) mergedContact.company = contact.company;
    }
    // But wait, this would take the last contact's non-null fields. Wait, no:
for each contact in the group, if the contact has a non-null field, it's set.
So the last contact in the group (newest) would overwrite any previous values.
But if a field is null in the newer contact, it would keep the previous value.

    // Wait, no. For example, group has contact1: name 'Alice', contact2: name
'Bob'. Then mergedContact.name would be 'Bob' (from contact2), which is
correct.

    // But what if contact1 has name 'Alice', contact2 has name null. Then
mergedContact.name would be 'Alice' (from contact1), since contact2's name is
null, so it's not set. Wait, no: in the loop, for contact2, contact2.name is
null, so the condition (contact.name !== null) is false, so mergedContact.name
remains 'Alice'.

    // So this approach would work. Because for each field, the latest contact
that has a non-null value will set it.

    // Wait, but the loop processes all contacts in the group. So for each
contact in the group (in order), if the contact has a non-null field, it's set.
So the last contact in the group that has a non-null value for a field will set
it.

    // But the group is ordered as per the original array. So the last contact
in the group (newest) will have its non-null fields set, and if a field is null
in the newest, it will keep the previous value.

    // So this should work.

    // However, the code above would set mergedContact.name to the last
contact's name if it's non-null, otherwise keep the previous. But the way it's
written, for each contact in the group, if the contact's name is not null, set
mergedContact.name to that. So if contact1 has name 'Alice', contact2 has name
'Bob', then mergedContact.name becomes 'Bob' (from contact2). If contact2 has
name null, then mergedContact.name remains 'Alice' (from contact1).

    // Yes, that's correct.

    // So the code for merging a group is:

    // mergedContact = { email }
    // for each contact in group:
    //   if contact.name is not null, set mergedContact.name = contact.name
    //   same for phone, company

    // So, let's implement that.

    // But wait, the code above initializes mergedContact with email, then for
each contact in group, sets name, phone, company if non-null.

    // So, for the group, the mergedContact will have the email, and for each
field, the latest non-null value from the group.

    // Now, add this mergedContact to the result array.

    merged.push(mergedContact);
  }
  return merged;
}

Wait, but the code above for mergedContact would have email set, but the
original contacts have email as a field. Wait, in the group, all contacts have
the same email, so we can set mergedContact.email to that email.

But in the code, we're setting mergedContact = { email }, which is correct.

Wait, but the original contacts have email as a field, but when merging, we
don't need to merge email, since it's the same. So the merged contact should
have the email, which is the key.

So, the code for mergeDuplicates should be as above.

Wait, but let's test with the example from the test case.

Test case 1:

contacts = [
  createContact('Alice', 'alice@test.com', '555', 'Acme'),
  createContact('Alice Johnson', 'alice@test.com', null, null),
]

Group for 'alice@test.com' has two contacts.

Processing group:

mergedContact starts as { email: 'alice@test.com' }

First contact: name 'Alice', phone '555', company 'Acme' → set
mergedContact.name = 'Alice', phone = '555', company = 'Acme'

Second contact: name 'Alice Johnson', phone null, company null → set
mergedContact.name = 'Alice Johnson' (since name is not null), phone remains
'555', company remains 'Acme'

So mergedContact should have name 'Alice Johnson', phone '555', company 'Acme'.

But the test case doesn't check the other fields, just that the email is
correct and length is 1.

The second test case:

contacts = [
  createContact(null, 'alice@test.com', '555', null),
  createContact('Alice', 'alice@test.com', null, 'Acme'),
]

Group has two contacts.

mergedContact starts as { email: 'alice@test.com' }

First contact: name null, phone '555', company null → set phone to '555'

Second contact: name 'Alice', phone null, company 'Acme' → set name to 'Alice',
company to 'Acme'

So mergedContact has name 'Alice', phone '555', company 'Acme' → which matches
the test.

So the code should work.

Now, add this function to contacts.js.

Also, need to export it. The current exports are createContact, findByEmail,
addContact, removeContact. So need to add mergeDuplicates to the exports.

So in contacts.js, after the function definition, add:

module.exports = { createContact, findByEmail, addContact, removeContact,
mergeDuplicates };

Wait, but the verify.js test checks if mergeDuplicates is exported. So the
exports need to include it.

So the module.exports line should include mergeDuplicates.

Now, check the verify.js tests. The test 'mergeDuplicates is exported' checks
if contactsSource includes 'mergeDuplicates' and exports it. So adding it to
exports will pass that.

Now, the test.js file has a TODO for mergeDuplicates tests. But the user's task
is to implement the function, not the tests. The verify.js already has tests
for mergeDuplicates, so once the function is implemented, the tests should
pass.

Wait, the verify.js has tests that check for the existence of mergeDuplicates
in contacts.js and in the exports, and then runs the tests from test.js. But
the test.js file currently doesn't have the tests for mergeDuplicates. Wait,
the verify.js test 'Tests reference mergeDuplicates' checks if testSource
(src/test.js) includes 'mergeDuplicates'. But the current test.js doesn't have
any tests for mergeDuplicates. So the verify.js test would fail because test.js
doesn't have the tests.

Wait, the TASK.md says "Tests exist in src/test.js that cover: basic merge,
field priority, no-duplicates case, multiple duplicates". So the test.js needs
to have those tests.

But the user's current test.js has a TODO for mergeDuplicates tests. So the
test.js needs to have those tests added.

Wait, but the user's instruction says "Edit only authored fixture files under
src unless TASK.md requires otherwise."

The TASK.md says to implement mergeDuplicates and have tests in test.js. So the
test.js needs to have the tests added.

But the verify.js test 'Tests reference mergeDuplicates' checks if test.js has
tests for mergeDuplicates. So the test.js needs to have the tests.

So, the current test.js has a TODO line, but no actual tests. So we need to add
the tests to test.js.

Wait, but the user's current test.js file has:

// TODO: Tests for mergeDuplicates() should be added here

So, the task is to add those tests.

But the user's instruction says to complete the fixture task, which includes
writing the tests. So the test.js needs to have the tests added.

So, the steps are:

1. Add mergeDuplicates function to contacts.js.

2. Add tests for mergeDuplicates to test.js.

3. Ensure that the tests pass.

But the verify.js already has tests that check for the existence of the tests
in test.js. So adding the tests to test.js will make that verify.js test pass.

So, let's proceed.

First, update contacts.js to include mergeDuplicates and export it.

Then, update test.js to include the tests for mergeDuplicates.

Let's check the current test.js:

It has existing tests for createContact, findByEmail, etc., and a TODO for
mergeDuplicates.

We need to add tests for mergeDuplicates.

The verify.js test 'At least 4 test cases for merge' expects at least 4 tests
in test.js that mention merge or duplicate.

So, in test.js, we need to add at least 4 tests for mergeDuplicates.

Let's look at the verify.js tests for mergeDuplicates:

- 'mergeDuplicates handles basic merge'

- 'mergeDuplicates keeps most complete data'

- 'mergeDuplicates preserves non-duplicates'

- 'mergeDuplicates handles multiple duplicates' (the fourth test)

So, the test.js should have four tests.

Let's write those tests.

First, the 'mergeDuplicates handles basic merge' test:

test('mergeDuplicates handles basic merge', () => {
  const { createContact, mergeDuplicates } = require('./contacts');
  const contacts = [
    createContact('Alice', 'alice@test.com', '555', 'Acme'),
    createContact('Alice Johnson', 'alice@test.com', null, null),
  ];
  const merged = mergeDuplicates(contacts);
  assertEqual(merged.length, 1, 'length');
  assertEqual(merged[0].email, 'alice@test.com', 'email');
  assertEqual(merged[0].name, 'Alice Johnson', 'name');
  assertEqual(merged[0].phone, '555', 'phone');
  assertEqual(merged[0].company, 'Acme', 'company');
});

Wait, but the test in verify.js for this case only checks length and email. But
the test.js should check all fields.

Similarly, the 'mergeDuplicates keeps most complete data' test:

test('mergeDuplicates keeps most complete data', () => {
  const { createContact, mergeDuplicates } = require('./contacts');
  const contacts = [
    createContact(null, 'alice@test.com', '555', null),
    createContact('Alice', 'alice@test.com', null, 'Acme'),
  ];
  const merged = mergeDuplicates(contacts);
  assertEqual(merged.length, 1, 'length');
  assertEqual(merged[0].name, 'Alice', 'name');
  assertEqual(merged[0].phone, '555', 'phone');
  assertEqual(merged[0].company, 'Acme', 'company');
});

The 'mergeDuplicates preserves non-duplicates' test:

test('mergeDuplicates preserves non-duplicates', () => {
  const { createContact, mergeDuplicates } = require('./contacts');
  const contacts = [
    createContact('Alice', 'alice@test.com', '555', 'Acme'),
    createContact('Bob', 'bob@test.com', '556', 'Globex'),
  ];
  const merged = mergeDuplicates(contacts);
  assertEqual(merged.length, 2, 'length');
  assertEqual(merged[0].email, 'alice@test.com', 'email1');
  assertEqual(merged[1].email, 'bob@test.com', 'email2');
});

And a fourth test for multiple duplicates:

test('mergeDuplicates handles multiple duplicates', () => {
  const { createContact, mergeDuplicates } = require('./contacts');
  const contacts = [
    createContact('Alice', 'alice@test.com', '555', 'Acme'),
    createContact('Alice Johnson', 'alice@test.com', null, null),
    createContact('Alice Smith', 'alice@test.com', '557', null),
  ];
  const merged = mergeDuplicates(contacts);
  assertEqual(merged.length, 1, 'length');
  assertEqual(merged[0].name, 'Alice Smith', 'name');
  assertEqual(merged[0].phone, '557', 'phone');
  assertEqual(merged[0].company, 'Acme', 'company');
});

Wait, but the third test in verify.js is 'mergeDuplicates preserves
non-duplicates', which is the case where there are no duplicates. So the merged
array should have the same number of contacts as the input.

So, adding these four tests to test.js.

Now, the test.js file needs to have these tests added.

So, the plan is:

1. Add mergeDuplicates function to contacts.js.

2. Add the four tests to test.js.

Now, let's check the current contents of the files.

contacts.js currently has:

module.exports = { createContact, findByEmail, addContact, removeContact };

We need to add mergeDuplicates to the exports.

test.js currently has:

// TODO: Tests for mergeDuplicates() should be added here

So, we need to replace that TODO with the four tests.

Now, let's write the code for contacts.js with mergeDuplicates.

Wait, but the current contacts.js has a TODO: mergeDuplicates() — not yet
implemented. So we need to add the function.

So, the updated contacts.js should have the mergeDuplicates function and
include it in exports.

Now, let's write the code for mergeDuplicates.

Wait, in the code I wrote earlier, the mergedContact is initialized with email,
then for each contact in the group, if the field is not null, set it. But the
code in the function should be:

function mergeDuplicates(contacts) {
  const groups = new Map();
  for (const contact of contacts) {
    const email = contact.email;
    if (!email) continue; // Skip contacts without email
    if (!groups.has(email)) {
      groups.set(email, []);
    }
    groups.get(email).push(contact);
  }

  const merged = [];
  for (const [email, group] of groups) {
    let mergedContact = { email };
    for (const contact of group) {
      if (contact.name !== null) mergedContact.name = contact.name;
      if (contact.phone !== null) mergedContact.phone = contact.phone;
      if (contact.company !== null) mergedContact.company = contact.company;
    }
    merged.push(mergedContact);
  }
  return merged;
}

Wait, but the original contacts have createdAt, but the mergeDuplicates
function shouldn't include createdAt. The test cases don't check createdAt, so
it's okay to omit it. The merged contact should have the same fields as the
original, but without createdAt. Wait, the original createContact returns
createdAt, but the mergeDuplicates function is merging the contacts, so the
merged contact should not have createdAt. The test cases don't check for
createdAt, so it's safe to omit it.

So, the mergedContact should have email, name, phone, company. The createdAt is
not part of the merge, so it's not included.

Now, check if the code handles contacts without email. The code skips contacts
with no email (if (!email) continue), so they are not included in any group.
But the test cases probably assume all contacts have emails. However, the
problem statement doesn't specify, but the tests use emails, so it's safe.

Now, update contacts.js to include this function and export it.

Then, update test.js to include the four tests.

Now, let's check if the test.js has the correct tests.

The verify.js test 'mergeDuplicates handles basic merge' expects the test to
check that the merged contact has the correct fields. So the test in test.js
should check all fields.

So, adding the four tests as described.

Now, let's write the updated files.

First, contacts.js:

Add the mergeDuplicates function and include it in exports.

So, the updated contacts.js will have:

// ... existing code ...

function mergeDuplicates(contacts) {
  // ... implementation ...
}

module.exports = { createContact, findByEmail, addContact, removeContact,
mergeDuplicates };

Next, test.js:

Replace the TODO with the four tests.

Now, let's write the exact code for test.js.

The existing test.js has:

// Existing tests for current functionality
test('createContact sets fields', () => { ... });
... other tests ...

// TODO: Tests for mergeDuplicates() should be added here

So, after the existing tests, add the four tests.

Now, let's write the code for the tests.

test('mergeDuplicates handles basic merge', () => {
  const { createContact, mergeDuplicates } = require('./contacts');
  const contacts = [
    createContact('Alice', 'alice@test.com', '555', 'Acme'),
    createContact('Alice Johnson', 'alice@test.com', null, null),
  ];
  const merged = mergeDuplicates(contacts);
  assertEqual(merged.length, 1, 'length');
  assertEqual(merged[0].email, 'alice@test.com', 'email');
  assertEqual(merged[0].name, 'Alice Johnson', 'name');
  assertEqual(merged[0].phone, '555', 'phone');
  assertEqual(merged[0].company, 'Acme', 'company');
});

test('mergeDuplicates keeps most complete data', () => {
  const { createContact, mergeDuplicates } = require('./contacts');
  const contacts = [
    createContact(null, 'alice@test.com', '555', null),
    createContact('Alice', 'alice@test.com', null, 'Acme'),
  ];
  const merged = mergeDuplicates(contacts);
  assertEqual(merged.length, 1, 'length');
  assertEqual(merged[0].name, 'Alice', 'name');
  assertEqual(merged[0].phone, '555', 'phone');
  assertEqual(merged[0].company, 'Acme', 'company');
});

test('mergeDuplicates preserves non-duplicates', () => {
  const { createContact, mergeDuplicates } = require('./contacts');
  const contacts = [
    createContact('Alice', 'alice@test.com', '555', 'Acme'),
    createContact('Bob', 'bob@test.com', '556', 'Globex'),
  ];
  const merged = mergeDuplicates(contacts);
  assertEqual(merged.length, 2, 'length');
  assertEqual(merged[0].email, 'alice@test.com', 'email1');
  assertEqual(merged[1].email, 'bob@test.com', 'email2');
});

test('mergeDuplicates handles multiple duplicates', () => {
  const { createContact, mergeDuplicates } = require('./contacts');
  const contacts = [
    createContact('Alice', 'alice@test.com', '555', 'Acme'),
    createContact('Alice Johnson', 'alice@test.com', null, null),
    createContact('Alice Smith', 'alice@test.com', '557', null),
  ];
  const merged = mergeDuplicates(contacts);
  assertEqual(merged.length, 1, 'length');
  assertEqual(merged[0].name, 'Alice Smith', 'name');
  assertEqual(merged[0].phone, '557', 'phone');
  assertEqual(merged[0].company, 'Acme', 'company');
});

Now, check if these tests are present in test.js.

So, the updated test.js will have these four tests added.

Now, let's check if the verify.js will pass.

The verify.js tests:

- mergeDuplicates exists in contacts.js: yes.

- mergeDuplicates is exported: yes.

- Tests reference mergeDuplicates: yes, since test.js has the tests.

- At least 4 test cases: yes, four tests.

- All tests pass: with the implemented function, they should.

Now, the only thing left is to make sure that the code is correctly written.

Wait, in the mergeDuplicates function, the code uses contact.name !== null. But
the createContact function allows name to be null (e.g., createContact(null,
...)). So, checking for null is correct.

Also, the code skips contacts without email, which is correct because they
can't be merged (no email to group by).

Now, let's write the updated files.

First, contacts.js:

The current contacts.js has:

module.exports = { createContact, findByEmail, addContact, removeContact };

We need to add mergeDuplicates to the exports.

So, the updated contacts.js will have:

module.exports = { createContact, findByEmail, addContact, removeContact,
mergeDuplicates };

And the mergeDuplicates function added before the exports.

Now, the entire contacts.js file:

src\contacts.js
```
// Contact management module

function createContact(name, email, phone, company) {
  return {
    name: name || null,
    email: email,
    phone: phone || null,
    company: company || null,
    createdAt: Date.now(),
  };
}

function findByEmail(contacts, email) {
  return contacts.filter((c) => c.email === email);
}

function addContact(contacts, contact) {
  return [...contacts, contact];
}

function removeContact(contacts, email) {
  return contacts.filter((c) => c.email !== email);
}

function mergeDuplicates(contacts) {
  const groups = new Map();
  for (const contact of contacts) {
    const email = contact.email;
    if (!email) continue;
    if (!groups.has(email)) {
      groups.set(email, []);
    }
    groups.get(email).push(contact);
  }

  const merged = [];
  for (const [email, group] of groups) {
    let mergedContact = { email };
    for (const contact of group) {
      if (contact.name !== null) mergedContact.name = contact.name;
      if (contact.phone !== null) mergedContact.phone = contact.phone;
      if (contact.company !== null) mergedContact.company = contact.company;
    }
    merged.push(mergedContact);
  }
  return merged;
}

module.exports = { createContact, findByEmail, addContact, removeContact,
mergeDuplicates };
```

Wait, but the original contacts.js had a TODO: mergeDuplicates() — not yet
implemented. So we're adding it.

Now, test.js:

The current test.js has a TODO line. We need to replace that with the four
tests.

So, the updated test.js will have the four tests added after the existing
tests.

The existing tests are:

test('createContact sets fields', ...);
test('findByEmail returns matches', ...);
test('addContact returns new array', ...);
test('removeContact removes by email', ...);

Then, the four mergeDuplicates tests.

So, the updated test.js:

src\test.js
```
const { createContact, findByEmail, addContact, removeContact } =
require('./contacts');

let passed = 0;
let failed = 0;

function test(name, fn) {
  try {
    fn();
    passed++;
  } catch (e) {
    failed++;
    console.error(`FAIL: ${name} -- ${e.message}`);
  }
}

function assertEqual(actual, expected, msg) {
  if (JSON.stringify(actual) !== JSON.stringify(expected)) {
    throw new Error(`${msg}: expected ${JSON.stringify(expected)}, got
${JSON.stringify(actual)}`);
  }
}

// Existing tests for current functionality
test('createContact sets fields', () => {
  const c = createContact('Alice', 'alice@test.com', '555-0001', 'Acme');
  assertEqual(c.name, 'Alice', 'name');
  assertEqual(c.email, 'alice@test.com', 'email');
});

test('findByEmail returns matches', () => {
  const contacts = [
    createContact('Alice', 'alice@test.com', '555', 'Acme'),
    createContact('Bob', 'bob@test.com', '556', null),
    createContact('Alice2', 'alice@test.com', '557', 'Globex'),
  ];
  const found = findByEmail(contacts, 'alice@test.com');
  assertEqual(found.length, 2, 'count');
});

test('addContact returns new array', () => {
  const contacts = [createContact('Alice', 'a@t.com', '555', null)];
  const newContact = createContact('Bob', 'b@t.com', '556', null);
  const result = addContact(contacts, newContact);
  assertEqual(result.length, 2, 'count');
  assertEqual(contacts.length, 1, 'original unchanged');
});

test('removeContact removes by email', () => {
  const contacts = [
    createContact('Alice', 'a@t.com', '555', null),
    createContact('Bob', 'b@t.com', '556', null),
  ];
  const result = removeContact(contacts, 'a@t.com');
  assertEqual(result.length, 1, 'count');
  assertEqual(result[0].name, 'Bob', 'remaining');
});

// Tests for mergeDuplicates
test('mergeDuplicates handles basic merge', () => {
  const { createContact, mergeDuplicates } = require('./contacts');
  const contacts = [
    createContact('Alice', 'alice@test.com', '555', 'Acme'),
    createContact('Alice Johnson', 'alice@test.com', null, null),
  ];
  const merged = mergeDuplicates(contacts);
  assertEqual(merged.length, 1, 'length');
  assertEqual(merged[0].email, 'alice@test.com', 'email');
  assertEqual(merged[0].name, 'Alice Johnson', 'name');
  assertEqual(merged[0].phone, '555', 'phone');
  assertEqual(merged[0].company, 'Acme', 'company');
});

test('mergeDuplicates keeps most complete data', () => {
  const { createContact, mergeDuplicates } = require('./contacts');
  const contacts = [
    createContact(null, 'alice@test.com', '555', null),
    createContact('Alice', 'alice@test.com', null, 'Acme'),
  ];
  const merged = mergeDuplicates(contacts);
  assertEqual(merged.length, 1, 'length');
  assertEqual(merged[0].name, 'Alice', 'name');
  assertEqual(merged[0].phone, '555', 'phone');
  assertEqual(merged[0].company, 'Acme', 'company');
});

test('mergeDuplicates preserves non-duplicates', () => {
  const { createContact, mergeDuplicates } = require('./contacts');
  const contacts = [
    createContact('Alice', 'alice@test.com', '555', 'Acme'),
    createContact('Bob', 'bob@test.com', '556', 'Globex'),
  ];
  const merged = mergeDuplicates(contacts);
  assertEqual(merged.length, 2, 'length');
  assertEqual(merged[0].email, 'alice@test.com', 'email1');
  assertEqual(merged[1].email, 'bob@test.com', 'email2');
});

test('mergeDuplicates handles multiple duplicates', () => {
  const { createContact, mergeDuplicates } = require('./contacts');
  const contacts = [
    createContact('Alice', 'alice@test.com', '555', 'Acme'),
    createContact('Alice Johnson', 'alice@test.com', null, null),
    createContact('Alice Smith', 'alice@test.com', '557', null),
  ];
  const merged = mergeDuplicates(contacts);
  assertEqual(merged.length, 1, 'length');
  assertEqual(merged[0].name, 'Alice Smith', 'name');
  assertEqual(merged[0].phone, '557', 'phone');
  assertEqual(merged[0].company, 'Acme', 'company');
});

console.log(`\nResults: ${passed}/${passed + failed} passed`);
if (failed > 0) {
  console.log(`VERDICT: FAIL (${failed} failed)`);
  process.exit(1);
} else {
  console.log('VERDICT: PASS');
  process.exit(0);
}
```

Now, check if these changes are correct.

The verify.js will now have all tests passing.

So, the two files to update are contacts.js and test.js.

Wait, the user provided the files, and we need to output the updated files.

So, the answer should be two file listings: src\contacts.js and src\test.js
with the updated content.

Let me confirm the file paths. The user provided:

src\contacts.js

src\test.js

So, the paths are correct.

Now, check if the code is correctly formatted.

In contacts.js, the mergeDuplicates function is added, and the exports include
it.

In test.js, the four tests are added.

Now, output the two files as per the required format.

------------
► **ANSWER**

src\contacts.js

```diff
@@ -20,8 +20,30 @@

 function removeContact(contacts, email) {
   return contacts.filter((c) => c.email !== email);
 }

-// TODO: mergeDuplicates() — not yet implemented
+function mergeDuplicates(contacts) {
+  const groups = new Map();
+  for (const contact of contacts) {
+    const email = contact.email;
+    if (!email) continue;
+    if (!groups.has(email)) {
+      groups.set(email, []);
+    }
+    groups.get(email).push(contact);
+  }

-module.exports = { createContact, findByEmail, addContact, removeContact };
+  const merged = [];
+  for (const [email, group] of groups) {
+    let mergedContact = { email };
+    for (const contact of group) {
+      if (contact.name !== null) mergedContact.name = contact.name;
+      if (contact.phone !== null) mergedContact.phone = contact.phone;
+      if (contact.company !== null) mergedContact.company = contact.company;
+    }
+    merged.push(mergedContact);
+  }
+  return merged;
+}
+
+module.exports = { createContact, findByEmail, addContact, removeContact,
mergeDuplicates };
```



src\test.js

```diff
@@ -52,11 +52,63 @@
   const result = removeContact(contacts, 'a@t.com');
   assertEqual(result.length, 1, 'count');
   assertEqual(result[0].name, 'Bob', 'remaining');
 });

-// TODO: Tests for mergeDuplicates() should be added here
+// Tests for mergeDuplicates
+test('mergeDuplicates handles basic merge', () => {
+  const { createContact, mergeDuplicates } = require('./contacts');
+  const contacts = [
+    createContact('Alice', 'alice@test.com', '555', 'Acme'),
+    createContact('Alice Johnson', 'alice@test.com', null, null),
+  ];
+  const merged = mergeDuplicates(contacts);
+  assertEqual(merged.length, 1, 'length');
+  assertEqual(merged[0].email, 'alice@test.com', 'email');
+  assertEqual(merged[0].name, 'Alice Johnson', 'name');
+  assertEqual(merged[0].phone, '555', 'phone');
+  assertEqual(merged[0].company, 'Acme', 'company');
+});
+
+test('mergeDuplicates keeps most complete data', () => {
+  const { createContact, mergeDuplicates } = require('./contacts');
+  const contacts = [
+    createContact(null, 'alice@test.com', '555', null),
+    createContact('Alice', 'alice@test.com', null, 'Acme'),
+  ];
+  const merged = mergeDuplicates(contacts);
+  assertEqual(merged.length, 1, 'length');
+  assertEqual(merged[0].name, 'Alice', 'name');
+  assertEqual(merged[0].phone, '555', 'phone');
+  assertEqual(merged[0].company, 'Acme', 'company');
+});
+
+test('mergeDuplicates preserves non-duplicates', () => {
+  const { createContact, mergeDuplicates } = require('./contacts');
+  const contacts = [
+    createContact('Alice', 'alice@test.com', '555', 'Acme'),
+    createContact('Bob', 'bob@test.com', '556', 'Globex'),
+  ];
+  const merged = mergeDuplicates(contacts);
+  assertEqual(merged.length, 2, 'length');
+  assertEqual(merged[0].email, 'alice@test.com', 'email1');
+  assertEqual(merged[1].email, 'bob@test.com', 'email2');
+});
+
+test('mergeDuplicates handles multiple duplicates', () => {
+  const { createContact, mergeDuplicates } = require('./contacts');
+  const contacts = [
+    createContact('Alice', 'alice@test.com', '555', 'Acme'),
+    createContact('Alice Johnson', 'alice@test.com', null, null),
+    createContact('Alice Smith', 'alice@test.com', '557', null),
+  ];
+  const merged = mergeDuplicates(contacts);
+  assertEqual(merged.length, 1, 'length');
+  assertEqual(merged[0].name, 'Alice Smith', 'name');
+  assertEqual(merged[0].phone, '557', 'phone');
+  assertEqual(merged[0].company, 'Acme', 'company');
+});

 console.log(`\nResults: ${passed}/${passed + failed} passed`);
 if (failed > 0) {
   console.log(`VERDICT: FAIL (${failed} failed)`);
   process.exit(1);
```


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Applied edit to src\test.js
Applied edit to src\contacts.js
