Tracking a program and storing information in a data structure

General Usage
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I am relatively new to Julia (<1 year) and I am developing a tool for tracking floating point addition. I have set up my work as a package, here is a reduced MWE:

module TestModule

# used for storing information when addition is done
mutable struct Tracking
    lastResult::Float64
    info::String

    Tracking() = new(0, "default message")
end

# overloading of addition, t has default argument in case of none provided
function +(in1::Float64, in2::Float64, t::Tracking = Nothing)
    +(a, b) = Base.:+(a, b)

    t.info = "writing a string to t.info when addition is performed"
    t.lastResult = in1 + in2

    return in1 + in2
end

# run f() and track information in t
function execute(f::Function, t::Tracking)
    +(a, b) = TestModule.:+(a, b, t)
    f()
end

function report(t::Tracking)
    println("final value = ", t.lastResult)
    println(t.info)
end


end

The aim is that the user creates an instance of a Tracking struct, then runs their program with execute() and uses report() for feedback. For example I have created a script for testing.

using TestModule

# create a Tracking instance
tracking = TestModule.Tracking()

# void function that performs whatever we want to do, in this case sum of 1000 rands
function myExperiment()
    n = 1000
    x = rand(n)
    sum = 0
    for k in 1:n
        sum += x[k]
    end
    println(sum)
end

# run and report
TestModule.execute(myExperiment, tracking)
TestModule.report(tracking)

I have my TestModule package configured, then the second file is a script in a separate file.
When I run the second file as a script, I want the fields of tracking to have changed, however the return is instead:

505.3979219546986
final value = 0.0
default message

The values of tracking aren’t being updated. I assume this is normal behaviour, so is there a way I can modify my code in order for the instance of my data structure to be updated as the program runs?