If Controller in JMeter

If Controller is one of the most important controllers. In JMeter, the “If Controller” is used to execute its child elements only when a specified condition evaluates to true. To evaluate all child elements under the “If Controller,” we can use a combination of a condition and well-designed child elements.

Here’s an example:

Scenario: Execute All Children If a Condition is True Suppose we want to execute three HTTP requests under the “If Controller” only if a variable executeCondition is set to “true”.

Test Plan Structure

Test Plan
- Thread Group
    If Controller (Condition: ${executeCondition} == "true")
        - HTTP Request 1
        - HTTP Request 2
        - HTTP Request 3

Steps to Create This:

Step 1: Add a Thread Group:

• Right-click the Test Plan → Add → Threads (Users) → Thread Group.

  Step 2: Add a User Defined Variables:

• Right-click the Thread Group → Add → Config Element → User Defined Variables.
• Add a variable, e.g., executeCondition, and set its value to true.

  Step 3: Add an If Controller:

• Right-click the Thread Group → Add → Logic Controller → If Controller.
• Set the condition to ${executeCondition} == "true.

  Step 4: Add HTTP Request Samplers:

• Right-click the If Controller → Add → Sampler → HTTP Request.
• Create three HTTP requests (or any other child elements).

Example

Here I give you the example cases to practice the condition scripting: In the If Controller’s “Condition” field, you would enter:

${__groovy(vars.get("userType") == "admin")}

This condition checks if the variable executeCondition is equal to “true”. If the condition evaluates to true, all child HTTP Request samplers will execute.

Output Example:

• If executeCondition = true: JMeter runs HTTP Request 1, HTTP Request 2, and HTTP Request 3.
• If executeCondition = false: JMeter skips all child elements under the “If Controller.” Notes:
• Ensure proper scoping of variables to avoid conflicts.
• Use Debug Sampler to verify variable values during test runs.

Explain about: Evaluate for All Children option

The “Evaluate for All Children” option in JMeter’s If Controller determines how the condition is evaluated when the controller has multiple child elements. Here’s a detailed explanation with examples of what happens when this option is checked or unchecked:

Scenario Setup: You want to execute some child elements (e.g., HTTP Requests) under an If Controller based on a condition, and you want to observe how enabling or disabling “Evaluate for All Children” impacts execution.

We have the example Test Plan

Thread Group
    User Defined Variables
    myVar = 1
    If Controller (Condition: ${myVar} < 3)
    HTTP Request 1
    HTTP Request 2

When “Evaluate for All Children” is Unchecked (Default Behavior)

• The condition is evaluated once when the If Controller is reached.
• If the condition evaluates to true, all children are executed sequentially.
• If the condition evaluates to false, none of the children are executed. Example:
• Initial Value of myVar: 1.
• Condition: ${myVar} < 3.

Execution Flow:

1. The condition ${myVar} < 3 is evaluated when the If Controller is reached: True (1 < 3).
2. Both HTTP Request 1 and HTTP Request 2 are executed.
3. If myVar is updated by one of the child elements (e.g., a PostProcessor modifies it), the new value does not affect the execution of subsequent children.

When “Evaluate for All Children” is Checked

• The condition is evaluated before each child is executed.
• If the condition becomes false during execution (e.g., due to a variable update), subsequent children are skipped. Example:
• Initial Value of myVar: 1.
• Condition: ${myVar} < 3.

Execution Flow:

1. The condition ${myVar} < 3 is evaluated before executing HTTP Request 1: True (1 < 3), so HTTP Request 1 is executed.
2. Suppose HTTP Request 1 updates myVar to 4 (e.g., using a PostProcessor or JSR223 script).
3. The condition is re-evaluated before executing HTTP Request 2: False (4 < 3), so HTTP Request 2 is skipped.

Use Case Examples:

• Unchecked: Use this when you want a consistent execution of all children once the condition is met, regardless of variable changes during execution.
• Checked: Use this when you want dynamic behavior where children are skipped if the condition changes during execution.