Question regarding t.test

Hello, I tried to repeat what was done in the video using the following code:

library(tidyverse)

data <- read.csv('independent-samples.csv')

data <- gather(data, Engineering, Management, key = 'Course', value = 'Grades')

t.test(data~Course, data = data, mu = -4)

Then after the last line of code using t.test, it came out to an error message:
Error in model.frame.default(formula = data ~ Course, data = data) :
  invalid type (list) for variable 'data'
Could you please help me look at this code? Thank you very much.