Add command filter Module API tests.

tests/modules/commandfilter.tcl

+set testmodule [file normalize src/modules/hellofilter.so]
+
+start_server {tags {"modules"}} {
+    r module load $testmodule log-key
+
+    test {Command Filter handles redirected commands} {
+        r set mykey @log
+        r lrange log-key 0 -1
+    } "{hellofilter.log set mykey @log}"
+
+    test {Command Filter can call RedisModule_CommandFilterArgDelete} {
+        r rpush mylist elem1 @delme elem2
+        r lrange mylist 0 -1
+    } {elem1 elem2}
+
+    test {Command Filter can call RedisModule_CommandFilterArgInsert} {
+        r del mylist
+        r rpush mylist elem1 @insertbefore elem2 @insertafter elem3
+        r lrange mylist 0 -1
+    } {elem1 --inserted-before-- @insertbefore elem2 @insertafter --inserted-after-- elem3}
+
+    test {Command Filter can call RedisModule_CommandFilterArgReplace} {
+        r del mylist
+        r rpush mylist elem1 @replaceme elem2
+        r lrange mylist 0 -1
+    } {elem1 --replaced-- elem2}
+} 

tests/test_helper.tcl

@@ -62,6 +62,7 @@ set ::all_tests {
     unit/lazyfree
     unit/wait
     unit/pendingquerybuf
+    modules/commandfilter
 }
 # Index to the next test to run in the ::all_tests list.
 set ::next_test 0