"what statistical test is used to test the significance of the correlation coefficient"

The hypothesis test is the name of the test which used to test the significance of correlation coefficient.

Hypothesis testing is the process in which two sets of statistical data are compared against a formed or designed set of data from an ideal model. A hypothesis is considered as null hypothesis statement in which no relationship find between two variables.

While on the other side, a hypothesis is considered as alternative hypothesis statement in which there is some statistical importance between two measured phenomenon’s.  

the historians cited in the article all agree with one another about the cause of the civil war. despite coming from different backgrounds and cultures, the historians agree that slavery was the root cause of the civil war. the fact that all these historiansgenerally agree with one another makes their shared viewpoints more reliable and valid, especially because the historians have different backgrounds and all work for the well-respected institutions of howard university, clemson university, and the university of colorado.