SETNX regression tests.

tests/unit/basic.tcl

@@ -138,21 +138,48 @@ start_server {tags {"basic"}} {
         r decrby novar 17179869185
     } {-1}
 
-    test {SETNX target key missing} {
-        r setnx novar2 foobared
-        r get novar2
-    } {foobared}
+    test "SETNX target key missing" {
+        r del novar
+        assert_equal 1 [r setnx novar foobared]
+        assert_equal "foobared" [r get novar]
+    }
 
-    test {SETNX target key exists} {
-        r setnx novar2 blabla
-        r get novar2
-    } {foobared}
+    test "SETNX target key exists" {
+        r set novar foobared
+        assert_equal 0 [r setnx novar blabla]
+        assert_equal "foobared" [r get novar]
+    }
 
-    test {SETNX against volatile key} {
+    test "SETNX against not-expired volatile key" {
         r set x 10
         r expire x 10000
-        list [r setnx x 20] [r get x]
-    } {0 10}
+        assert_equal 0 [r setnx x 20]
+        assert_equal 10 [r get x]
+    }
+
+    test "SETNX against expired volatile key" {
+        # Make it very unlikely for the key this test uses to be expired by the
+        # active expiry cycle. This is tightly coupled to the implementation of
+        # active expiry and dbAdd() but currently the only way to test that
+        # SETNX expires a key when it should have been.
+        for {set x 0} {$x < 9999} {incr x} {
+            r setex key-$x 3600 value
+        }
+
+        # This will be one of 10000 expiring keys. A cycle is executed every
+        # 100ms, sampling 10 keys for being expired or not.  This key will be
+        # expired for at most 1s when we wait 2s, resulting in a total sample
+        # of 100 keys. The probability of the success of this test being a
+        # false positive is therefore approx. 1%.
+        r set x 10
+        r expire x 1
+
+        # Wait for the key to expire
+        after 2000
+
+        assert_equal 1 [r setnx x 20]
+        assert_equal 20 [r get x]
+    }
 
     test {EXISTS} {
         set res {}