Data file with Newman in Postman

Introduction

Using a data file with Newman lets you run the same API tests many times with different inputs. This helps check if your API works well with various data.

You want to test an API with many user details like names and emails.

You need to check how your API handles different product IDs.

You want to run the same test steps but with different login credentials.

You want to automate testing for multiple scenarios without writing many tests.

You want to save time by running many tests in one go using a data file.

Syntax

Postman

newman run <collection-file.json> -d <data-file.json|csv>

The -d option tells Newman to use a data file for multiple test runs.

The data file can be JSON or CSV format with different sets of data.

Examples

Runs the collection using data from a JSON file named users.json.

Postman

newman run mycollection.json -d users.json

Runs the collection using data from a CSV file named data.csv.

Postman

newman run mycollection.json -d data.csv

Sample Program

This command runs the Postman collection sample_collection.json using the data in sample_data.json. Each row in the data file runs the tests once with that data.

Postman

newman run sample_collection.json -d sample_data.json

Important Notes

Make sure your data file keys match the variable names used in your Postman requests.

Use JSON for complex data and CSV for simple tabular data.

Newman runs one iteration per row in the data file.

Summary

Data files let you run the same tests with different inputs easily.

Newman supports JSON and CSV data files for this purpose.

Use the -d option with Newman to specify your data file.

Practice

1. What is the main purpose of using a data file with Newman when running Postman collections?

easy

A. To run the same tests multiple times with different input values

B. To speed up the execution of tests by caching responses

C. To generate reports automatically after test execution

D. To connect Newman to a database for live data

Solution

1. Step 1: Understand the role of data files in Newman

   Data files allow running the same test collection multiple times with different sets of input data.

2. Step 2: Identify the correct purpose

   This helps test how the API behaves with various inputs without rewriting tests.

3. Final Answer:

   To run the same tests multiple times with different input values -> Option A

4. Quick Check:

   Data files = multiple inputs for same tests [OK]

Hint: Data files = repeat tests with different inputs [OK]

Common Mistakes:

• Thinking data files speed up tests
• Confusing data files with report generation
• Assuming data files connect to databases

2. Which command correctly runs a Postman collection named api_tests.postman_collection.json with a data file named test_data.csv using Newman?

easy

A. newman run api_tests.postman_collection.json -d test_data.csv

B. newman run api_tests.postman_collection.json --data test_data.csv

C. newman execute api_tests.postman_collection.json -data test_data.csv

D. newman run api_tests.postman_collection.json -datafile test_data.csv

Solution

1. Step 1: Recall Newman syntax for data files

   Newman uses the -d option to specify a data file.

2. Step 2: Match the correct command

   newman run api_tests.postman_collection.json -d test_data.csv uses -d correctly with newman run and the file names.

3. Final Answer:

   newman run api_tests.postman_collection.json -d test_data.csv -> Option A

4. Quick Check:

   Use -d for data file in Newman [OK]

Hint: Use '-d' option to add data file in Newman command [OK]

Common Mistakes:

• Using '--data' instead of '-d'
• Using 'execute' instead of 'run'
• Typing '-datafile' which is invalid

3. Given a CSV data file users.csv with two rows:
username,password
alice,pass123
bob,pass456
and a Postman test collection that uses {{username}} and {{password}} variables, what will be the number of iterations Newman runs when executing with -d users.csv?

medium

A. 1 iteration

B. 0 iterations

C. 3 iterations

D. 2 iterations

Solution

1. Step 1: Count data rows excluding header

   The CSV has 3 lines: 1 header + 2 data rows (alice and bob).

2. Step 2: Understand iteration count in Newman

   Newman runs one iteration per data row, so 2 iterations for 2 users.

3. Final Answer:

   2 iterations -> Option D

4. Quick Check:

   Iterations = data rows (excluding header) [OK]

Hint: Iterations = number of data rows in file [OK]

Common Mistakes:

• Counting header row as iteration
• Assuming only 1 iteration always
• Confusing iterations with number of variables

4. You run Newman with -d data.json but get an error saying the data file format is invalid. Which of the following is the most likely cause?

medium

A. The CSV file was renamed to .json but still contains CSV data

B. The JSON file contains an array of objects but is missing a root array

C. The JSON file uses single quotes instead of double quotes for keys and strings

D. The data file is empty

Solution

1. Step 1: Check JSON format requirements

   JSON requires double quotes for keys and string values; single quotes cause parsing errors.

2. Step 2: Identify common JSON errors

   Using single quotes is a common mistake causing invalid format errors.

3. Final Answer:

   The JSON file uses single quotes instead of double quotes for keys and strings -> Option C

4. Quick Check:

   JSON needs double quotes, not single [OK]

Hint: JSON keys and strings must use double quotes [OK]

Common Mistakes:

• Ignoring JSON syntax rules
• Confusing CSV and JSON file contents
• Not checking for empty files

5. You want to run a Postman collection with Newman using a JSON data file that contains user details. The JSON file has this structure:

[
  {"username": "alice", "password": "pass123"},
  {"username": "bob", "password": "pass456"},
  {"username": "", "password": "pass789"}
]

What will happen during the third iteration when username is an empty string?

hard

A. Newman will throw a syntax error and stop execution

B. The test will run with an empty username, possibly causing failures if username is required

C. Newman will skip the third iteration automatically because username is empty

D. The third iteration will use the username from the previous iteration

Solution

1. Step 1: Understand how Newman handles empty values in data files

   Newman runs all iterations regardless of empty values; it does not skip or throw errors automatically.

2. Step 2: Consider test behavior with empty username

   If the test expects a username, an empty string may cause test failures or unexpected results.

3. Final Answer:

   The test will run with an empty username, possibly causing failures if username is required -> Option B

4. Quick Check:

   Empty data values run as-is, may cause test failures [OK]

Hint: Empty values run as-is; tests may fail if required [OK]

Common Mistakes:

• Assuming Newman skips empty data rows
• Expecting automatic errors for empty strings
• Thinking data repeats from previous iteration