Data Providers

Data Providers

Here’s a deep dive into TestNG’s @DataProvider feature, covering everything from basic syntax to advanced usages like inheritance and dynamic data based on the test method.

1. What Are DataProviders in TestNG?

A DataProvider is a factory for test data. It lets you feed the same @Test method with multiple sets of parameters, driving data-driven testing without duplicating test code.

2. DataProvider Syntax

@DataProvider(name = "myData")
public Object[][] myDataProviderMethod() {

  return new Object[][] {
    { /* first row */ val1, val2, … },
    { /* second row */ val1b, val2b, … },
    // …
  };
}

Return type:

• Object[][] (each sub-array is one invocation’s arguments)

• or Iterator<Object[]>

Name: defaults to the method name; you can override via name = “…”.

Optional parallelism: @DataProvider(name=”x”, parallel=true) runs rows in parallel threads.

3. How To Use DataProviders in TestNG

1. Define the provider method in the same class (or a separate utility class).

2. Annotate your test with dataProvider=”…”.

public class LoginTests {

  @DataProvider(name = "credentials")
  public Object[][] creds() {
    return new Object[][] {
      { "alice", "pass1" },
      { "bob",   "pass2" }
    };
  }

  @Test(dataProvider = "credentials")
  public void loginTest(String username, String password) {
    // This test runs twice:
    //  1) username="alice", password="pass1"
    //  2) username="bob",   password="pass2"
    performLogin(username, password);
    Assert.assertTrue(isLoggedIn());
  }
}

4. Inherited DataProviders

If you want to reuse providers across multiple test classes, you can:

A. In a superclass

public class BaseData {
  @DataProvider
  public Object[][] numbers() {
    return new Object[][] { {1},{2},{3} };
  }
}

public class MyTests extends BaseData {
  @Test(dataProvider = "numbers")
  public void testNumber(int n) {
    System.out.println("n = " + n);
  }
}

B. In a separate class

public class Utils {
  @DataProvider(name="users")
  public static Object[][] userProvider() { … }
}

public class UserTests {
  @Test(dataProvider="users", dataProviderClass=Utils.class)
  public void testUser(String username) { … }
}

5. MultiValue DataProviders

Any provider can supply multiple parameters per invocation by returning sub‐arrays with more elements:

@DataProvider(name = "calculatorData")
public Object[][] calcData() {
  return new Object[][] {
    // {a, b, expectedSum, expectedProduct}
    { 2, 3, 5, 6 },
    { 4, 5, 9, 20 }
  };
}

@Test(dataProvider = "calculatorData")
public void mathTest(int a, int b, int sum, int product) {
  Assert.assertEquals(a + b, sum);
  Assert.assertEquals(a * b, product);
}

6. DataProviders With Method As Parameter

You can make your provider dynamic by inspecting which test method is calling it:

@DataProvider(name = "dynamic")
public Object[][] dynamicProvider(Method m) {
  if (m.getName().equals("testA")) {
    return new Object[][] { {"A1"},{"A2"} };
  } else if (m.getName().equals("testB")) {
    return new Object[][] { {"B1"},{"B2"},{"B3"} };
  }
  return new Object[0][];
}

@Test(dataProvider = "dynamic")
public void testA(String data) { System.out.println("A: " + data); }

@Test(dataProvider = "dynamic")
public void testB(String data) { System.out.println("B: " + data); }

• Signature: provider must accept a java.lang.reflect.Method (and/or ITestContext) before returning the data.

• Allows you to tailor the data set per test.

Summary

• @DataProvider gives you a clean way to run a test multiple times with different inputs.

• You can inherit providers in superclasses or external classes (dataProviderClass).

• Providers can return multi-column data sets.

• By adding a Method parameter, you can dispatch different data to different tests from the same provider.

Use DataProviders for robust, maintainable, data-driven TestNG suites!