added some more unit tests and comments explaining the parts of the function that had been confusing to me

Author: UltraBob

cachematrix.R

@@ -5,9 +5,15 @@
 
 ## This function takes a matrix as an argument, and contains
 ## getters and setters for both the matrix itself, and the
-## inverse of the matrix.
+## inverse of the matrix. When the matrix is changed the
+## cache of the inverse matrix is cleared
 
 makeCacheMatrix <- function(x = matrix()) {
+    # I'll confess some minor scoping confusion.  I don't
+    # really understand what environment inverse is being
+    # created in and why it doesn't end up being shared
+    # by all instances of makeCacheMatrix, but I tested
+    # and it doesn't
     inverse <- NULL
     set <- function(y) {
         x <<- y
@@ -22,6 +28,11 @@ makeCacheMatrix <- function(x = matrix()) {
     getInverse <- function() {
         inverse
     }
+    # this list below was confusing to me before so I'm commenting
+    # to explain it to future me.  The last call in a function
+    # is the one that gets returned, so by returning this list,
+    # we are providing all the functions to the new object
+    # being created.
     list(set = set, get = get, 
          setInverse = setInverse, 
          getInverse = getInverse)

tests/1.R

@@ -6,18 +6,47 @@ test.MCM <- function() {
     testMatrix <- matrix(c(4,2,7,6),2,2)
     newmat <- matrix(c(1,2,3,4),2,2)
     testMCM <- makeCacheMatrix(testMatrix)
-    checkEquals(testMatrix, testMCM$get())
-    checkEquals(NULL,testMCM$getInverse())
+    #check that matrix is being set properly
+    checkEquals(testMatrix, testMCM$get()) #1
+    # check that inverse variable properly initialized to NULL
+    checkEquals(NULL,testMCM$getInverse()) #2
     testMCM$set(newmat)
-    checkEquals(newmat, testMCM$get())
-    checkEquals(NULL, testMCM$getInverse())
+    # check that setter is working properly
+    checkEquals(newmat, testMCM$get()) #3
+    # check that inverse stays null after set
+    checkEquals(NULL, testMCM$getInverse()) #4
     newSol <- cacheSolve(testMCM)
-    checkEquals(matrix(c(-2,1,1.5,-0.5),2,2),newSol)
-    checkEquals(newSol, testMCM$getInverse())
+    #check that cacheSolve gives the correct answer (matrix newmat)
+    checkEquals(matrix(c(-2,1,1.5,-0.5),2,2),newSol) #5
+    # check that there is now a value for inverse and that 
+    # getInverse works properly
+    checkEquals(newSol, testMCM$getInverse()) #6
     testMCM$set(testMatrix)
-    checkEquals(NULL,testMCM$getInverse())
+    # check that setting the matrix resets inverse to NULL
+    checkEquals(NULL,testMCM$getInverse()) #7
     testSol <- cacheSolve(testMCM)
-    checkEquals(matrix(c(0.6,-0.2,-0.7,0.4),2,2),testSol)
-    checkTrue(!is.null(testMCM$getInverse()))
-    checkEquals(testMCM$getInverse(),testSol)
+    # check for the correct answer with another matrix (testMatrix)
+    checkEquals(matrix(c(0.6,-0.2,-0.7,0.4),2,2),testSol) #8
+    # check that the inverse cache is now set
+    checkTrue(!is.null(testMCM$getInverse())) #9
+    # check that the cached value is correct
+    checkEquals(testMCM$getInverse(),testSol) #10
+    # this set of checks creates two makeCacheMatrix objects and
+    # checks to make sure their caches don't interfere
+    testMCM$set(testMatrix)
+    newMCM <- makeCacheMatrix(newmat)
+    checkTrue(is.null(testMCM$getInverse())) #11
+    checkTrue(is.null(newMCM$getInverse())) #12
+    checkTrue(is.null(newMCM$inverse)) #13
+    checkTrue(is.null(testMCM$inverse)) #14
+    cacheSolve(testMCM)
+    checkTrue(!is.null(testMCM$getInverse())) #15
+    checkTrue(is.null(newMCM$getInverse())) #16
+    # now we've confirmed that testMCM has a cached inverse
+    # and newMCM doesn't, and that the value of xxxMCM$inverse
+    # was null before, now we'll check that they were null
+    # because you can't pull the data out that way, not
+    # because the cache hadn't been set yet
+    checkTrue(is.null(testMCM$inverse)) #17
+    checkTrue(is.null(newMCM$inverse)) #18
 }