The test functions of general finite elements are like interpolation functions (if my understanding is correct). But how about test functions of Raviart-Thomas elements?
Let's raise the $RT0$ element as an example. The test functions of the three edges are
$\phi_1 = \sqrt{2}\left(\hat{x_1} \quad \hat{x_2}\right)^{T}, \phi_2 = \left(-1+\hat{x_1} \quad \hat{x_2}\right)^{T}, \text{ and } \phi_3 = \left(\hat{x_1} \quad -1+\hat{x_2}\right)^{T}$,
where $\hat{x_1} \text{ and } \hat{x_2}$ are coodinates of a reference triangular element (as shown in the figure below).
We can calculate the $\hat{x_1} \text{ and } \hat{x_2}$ based on the coordinates of original elements, i.e. ${x_1} \text{ and } {x_2}$.
But, what is the physical meaning of the test functions of RT element? I think they are not like interpolation functions. They just kind of link to the normal vectors of edges?