Add SparseDC tests

tests/testthat/test-sparseDC-simulate.R

+context("SparseDC simulation")
+
+test_that("SparseDC simulation output is valid", {
+    expect_true(validObject(sparseDCSimulate()))
+})

tests/testthat/test-sparseDCEstimate.R

+context("sparseDCEstimate")
+
+library(scater)
+data("sc_example_counts")
+
+test_that("sparseDCEstimate works", {
+    conditions <- sample(1:2, ncol(sc_example_counts), replace = TRUE)
+
+    params <- sparseDCEstimate(sc_example_counts, conditions,
+                               nclusters = 3)
+    expect_true(validObject(params))
+})