How to access dependsOnMethod or dependsOnGroup across different classes having TestNG tests?

We're writing a TestNG based regression suite. Soon, we'll have tests across different classes, wherein the Test in Class A should run only after tests in Class B has run, also we'll need a facility to access some methods, variables which will be common across.

I am getting nullpointer exception & few other issues when tried to build & access dependent tests spread across different classes.

public class BaseTest {
final  TestContext testContext = new TestContext();

TheUser newUser;
String newUserPhoneNumber;
String newUserVerificationCode;

public BaseTest() {
    newUser = testContext.getUserObjectManager().getTheUser();
    newUserPhoneNumber = newUser.generateRandomPhoneNumber();
    newUserVerificationCode = newUser.validVerificationCode();
}

@BeforeSuite
public void requestUserTokens(ITestContext iTestContext) {
    iTestContext.setAttribute("username", newUser.getUsername());
    iTestContext.setAttribute("username", newUser.getPassword());
}

}

Login Test

public class LoginTests extends BaseTest {
private POSTRequest postRequest;
private String password;
private String username;



@BeforeClass()
@BeforeEach
public void init() {
    newUser = testContext.getUserObjectManager().getTheUser();
    postRequest = new POSTRequest();
    postRequest.chooseEndPoint(OAUTH2_PARTIAL_PATH);
}

@Test(dependsOnGroups = {"SignupGroup"})
public void postRequestUserLogsInWithValidCredentials(ITestContext iTestContext) {
    JSONObject requestBody = new JSONObject();

    requestBody.put("client_id", "**********");
    requestBody.put("grant_type", "password");
    username = iTestContext.getAttribute("username").toString();
    password = iTestContext.getAttribute("password").toString();

    System.out.println("TestContext username--> " + newUser.getUsername());
    System.out.println("TestContext password--> " + newUser.getPassword());

    System.out.println("iTestContext username--> " + username);
    System.out.println("iTestContext password--> " + password);

.. ..}

SignUP Test

public class SignUpTests {
private final TheUser newUser = new TheUser();
String newUserPhoneNumber = newUser.generateRandomPhoneNumber();
String newUserVerificationCode = newUser.validVerificationCode();
private PUTRequest putrequest;
private POSTRequest postRequest;

@BeforeClass
@BeforeEach
public void init() {
    putrequest = new PUTRequest();
    postRequest = new POSTRequest();
    putrequest.chooseEndPoint(API_V1_PARTIAL_PATH);
    postRequest.chooseEndPoint(API_V1_PARTIAL_PATH);
}

@Test(priority = 0, groups = {"SignupGroup"})
public void userEntersInvalidVerificationCode() {
    String invalidVerificationCode = Helper.randomNumber(6);
    JSONObject requestBody = new JSONObject();
    requestBody.put("sms_code", invalidVerificationCode);
    String path = USERS_VERIFICATION_PHONE_NUMBER_PATH + newUser.getVerificationId() + "/";
    Response response = putrequest.putRequest(requestBody, path);

    assertThat(response.getStatusCode(), (anyOf(is(SC_UNPROCESSABLE_ENTITY), is(SC_FORBIDDEN))));
}

}

TestNG.xml

<!DOCTYPE suite SYSTEM "https://testng.org/testng-1.0.dtd" >

<test name="SignUp Test Suite" >
    <parameter name="Test without Mock" value="Api test-method Three" />
    <classes >
        <class name="signupAndLogin.SignUpTests" />
    </classes>
</test>

<test name="Login Test Suite">
    <parameter name="Test without Mock" value="Api test-method Three" />
    <groups>
        <dependencies>
            <group depends-on="SignupGroup" name="LoginTestsGroup"/>
        </dependencies>
    </groups>
    <classes>
        <class name="signupAndLogin.LoginTests" />
    </classes>
</test>

Kindly advise. Thanks in advance.

TestNG wants your files to be in same package.

Try to remove your

<groups>
        <dependencies>
            <group depends-on="SignupGroup" name="LoginTestsGroup"/>
        </dependencies>
    </groups>

And instead use the run element by including the group you want to run.

According to the documentation, https://testng.org/doc/documentation-main.html#test-groups

Your will look similar to

<test name="SignUp Test Suite" >
    <parameter name="Test without Mock" value="Api test-method Three" />
    <classes >
        <class name="signupAndLogin.SignUpTests" />
    </classes>
</test>

<test name="Login Test Suite">
    <parameter name="Test without Mock" value="Api test-method Three" />
    <groups>
      <run>
        <include name="SignupGroup" />
      </run>
    </groups>
    <classes>
        <class name="signupAndLogin.LoginTests" />
    </classes>
</test>

Helpful Example: https://howtodoinjava.com/testng/testng-test-groups/