Add test and example for Strain

Strain/StrainExample.elm

@@ -0,0 +1,9 @@
+module StrainExample where
+
+import List
+
+keep : (a -> Bool) -> List a ->  List a
+keep predicate list = List.filter predicate list
+
+discard : (a -> Bool) -> List a -> List a
+discard predicate list = (keep (\val -> not (predicate val)) list)

Strain/StrainTest.elm

@@ -0,0 +1,34 @@
+module StrainTest where
+
+-- TODO - remove example inclusion once Problem sets are ready to go live or CI is set up.
+
+import ElmTest.Test exposing (test, Test, suite)
+import ElmTest.Assertion exposing (assert, assertEqual)
+import ElmTest.Runner.Element exposing (runDisplay)
+
+import StrainExample exposing (keep, discard)
+
+import String
+
+even = \number -> number % 2 == 0
+odd = \number -> number % 2 == 1
+isFirstLetter = \letter-> \word -> (String.left 1 word) == letter
+lessThanTen = \num -> num < 10
+
+tests : Test
+tests = suite "Strain Test Suite"
+  [ test "empty keep" (assertEqual [] (keep lessThanTen [])),
+    test "keep everything" (assertEqual [1, 2, 3] (keep lessThanTen [1, 2, 3])),
+    test "keep first and last" (assertEqual [1, 3] (keep odd [1, 2, 3])),
+    test "keep nothing" (assertEqual [] (keep even [1,3,5,7])),
+    test "keep neither first nor last" (assertEqual [2] (keep even [1, 2, 3])),
+    test "keep strings" (assertEqual ["zebra", "zombies", "zealot"] (keep (isFirstLetter "z") ["apple", "zebra", "banana", "zombies", "cherimoya", "zealot"])),
+    test "empty discard" (assertEqual [] (discard lessThanTen [])),
+    test "discard everything" (assertEqual [] (discard lessThanTen [1, 2, 3])),
+    test "discard first and last" (assertEqual [2] (discard odd [1, 2, 3])),
+    test "discard nothing" (assertEqual [1,3,5,7] (discard even [1,3,5,7])),
+    test "discard neither first nor last" (assertEqual [1, 3] (discard even [1, 2, 3])),
+    test "discard strings" (assertEqual ["apple", "banana", "cherimoya"] (discard (isFirstLetter "z") ["apple", "zebra", "banana", "zombies", "cherimoya", "zealot"]))
+  ]
+
+main = runDisplay tests

elm-package.json

@@ -22,7 +22,8 @@
         "RNATranscription",
         "Sublist",
         "Bob",
-        "sumOfMultiples"
+        "SumOfMultiples",
+        "Strain"
     ],
     "exposed-modules": [],
     "dependencies": {