[MINOR][SPARKR] fix kstest example error and add unit test

## What changes were proposed in this pull request?

While adding vignettes for kstest, I found some errors in the example:
1. There is a typo of kstest;
2. print.summary.KStest doesn't work with the example;

Fix the example errors;
Add a new unit test for print.summary.KStest;

## How was this patch tested?
Manual test;
Add new unit test;

Author: [email protected] <[email protected]>

Closes apache#16259 from wangmiao1981/ks.

(cherry picked from commit f2ddabf)
Signed-off-by: Yanbo Liang <[email protected]>

Author: wangmiao1981

R/pkg/R/mllib.R

@@ -1595,14 +1595,14 @@ setMethod("write.ml", signature(object = "ALSModel", path = "character"),
 #' \dontrun{
 #' data <- data.frame(test = c(0.1, 0.15, 0.2, 0.3, 0.25))
 #' df <- createDataFrame(data)
-#' test <- spark.ktest(df, "test", "norm", c(0, 1))
+#' test <- spark.kstest(df, "test", "norm", c(0, 1))
 #'
 #' # get a summary of the test result
 #' testSummary <- summary(test)
 #' testSummary
 #'
 #' # print out the summary in an organized way
-#' print.summary.KSTest(test)
+#' print.summary.KSTest(testSummary)
 #' }
 #' @note spark.kstest since 2.1.0
 setMethod("spark.kstest", signature(data = "SparkDataFrame"),

R/pkg/inst/tests/testthat/test_mllib.R

@@ -986,6 +986,12 @@ test_that("spark.kstest", {
   expect_equal(stats$p.value, rStats$p.value, tolerance = 1e-4)
   expect_equal(stats$statistic, unname(rStats$statistic), tolerance = 1e-4)
   expect_match(capture.output(stats)[1], "Kolmogorov-Smirnov test summary:")
+
+  # Test print.summary.KSTest
+  printStats <- capture.output(print.summary.KSTest(stats))
+  expect_match(printStats[1], "Kolmogorov-Smirnov test summary:")
+  expect_match(printStats[5],
+               "Low presumption against null hypothesis: Sample follows theoretical distribution. ")
 })
 
 test_that("spark.randomForest", {