Fix #97, check event spec string

The fully-rendered strings are not entirely consistent, affected
by many external factors outside the control of the test cases.

There was even a warning in the comment against doing this, but
it was included nonetheless as an example of how it can be done.
This now keeps the original example but keeps it in the comment only,
and converts the actual test to follow the recommended practice of
only testing the spec/format string, not the fully-rendered string.

This should be much more stable going forward, and should work with
both CCSDS v1 and v2 configs.

unit-test/coveragetest/coveragetest_sample_app.c

@@ -48,7 +48,7 @@ typedef struct
 {
     uint16      ExpectedEvent;
     uint32      MatchCount;
-    const char *ExpectedText;
+    const char *ExpectedFormat;
 } UT_CheckEvent_t;
 
 /*
@@ -58,7 +58,6 @@ static int32 UT_CheckEvent_Hook(void *UserObj, int32 StubRetcode, uint32 CallCou
                                 va_list va)
 {
     UT_CheckEvent_t *State = UserObj;
-    char             TestText[CFE_MISSION_EVS_MAX_MESSAGE_LENGTH];
     uint16           EventId;
     const char *     Spec;
 
@@ -71,24 +70,34 @@ static int32 UT_CheckEvent_Hook(void *UserObj, int32 StubRetcode, uint32 CallCou
         EventId = UT_Hook_GetArgValueByName(Context, "EventID", uint16);
         if (EventId == State->ExpectedEvent)
         {
-            /*
-             * Example of how to validate the full argument set.
-             * If reference text was supplied, also check against this.
-             *
-             * NOTE: While this can be done, use with discretion - This isn't really
-             * verifying that the FSW code unit generated the correct event text,
-             * rather it is validating what the system snprintf() library function
-             * produces when passed the format string and args.
-             *
-             * __This derived string is not an actual output of the unit under test__
-             */
-            if (State->ExpectedText != NULL)
+            if (State->ExpectedFormat != NULL)
             {
                 Spec = UT_Hook_GetArgValueByName(Context, "Spec", const char *);
                 if (Spec != NULL)
                 {
-                    vsnprintf(TestText, sizeof(TestText), Spec, va);
-                    if (strcmp(TestText, State->ExpectedText) == 0)
+                    /*
+                     * Example of how to validate the full argument set.
+                     * ------------------------------------------------
+                     *
+                     * If really desired one can call something like:
+                     *
+                     * char TestText[CFE_MISSION_EVS_MAX_MESSAGE_LENGTH];
+                     * vsnprintf(TestText, sizeof(TestText), Spec, va);
+                     *
+                     * And then compare the output (TestText) to the expected fully-rendered string.
+                     *
+                     * NOTE: While this can be done, use with discretion - This isn't really
+                     * verifying that the FSW code unit generated the correct event text,
+                     * rather it is validating what the system snprintf() library function
+                     * produces when passed the format string and args.
+                     *
+                     * This type of check has been demonstrated to make tests very fragile,
+                     * because it is influenced by many factors outside the control of the
+                     * test case.
+                     *
+                     * __This derived string is not an actual output of the unit under test__
+                     */
+                    if (strcmp(Spec, State->ExpectedFormat) == 0)
                     {
                         ++State->MatchCount;
                     }
@@ -108,11 +117,11 @@ static int32 UT_CheckEvent_Hook(void *UserObj, int32 StubRetcode, uint32 CallCou
  * Helper function to set up for event checking
  * This attaches the hook function to CFE_EVS_SendEvent
  */
-static void UT_CheckEvent_Setup(UT_CheckEvent_t *Evt, uint16 ExpectedEvent, const char *ExpectedText)
+static void UT_CheckEvent_Setup(UT_CheckEvent_t *Evt, uint16 ExpectedEvent, const char *ExpectedFormat)
 {
     memset(Evt, 0, sizeof(*Evt));
     Evt->ExpectedEvent = ExpectedEvent;
-    Evt->ExpectedText  = ExpectedText;
+    Evt->ExpectedFormat = ExpectedFormat;
     UT_SetVaHookFunction(UT_KEY(CFE_EVS_SendEvent), UT_CheckEvent_Hook, Evt);
 }
 
@@ -272,7 +281,7 @@ void Test_SAMPLE_ProcessCommandPacket(void)
     UT_CheckEvent_t EventTest;
 
     memset(&TestMsg, 0, sizeof(TestMsg));
-    UT_CheckEvent_Setup(&EventTest, SAMPLE_INVALID_MSGID_ERR_EID, "SAMPLE: invalid command packet,MID = 0xffffffff");
+    UT_CheckEvent_Setup(&EventTest, SAMPLE_INVALID_MSGID_ERR_EID, "SAMPLE: invalid command packet,MID = 0x%x");
 
     /*
      * The CFE_SB_GetMsgId() stub uses a data buffer to hold the
@@ -351,7 +360,7 @@ void Test_SAMPLE_ProcessGroundCommand(void)
     SAMPLE_ProcessGroundCommand(&TestMsg.Base);
 
     /* test an invalid CC */
-    UT_CheckEvent_Setup(&EventTest, SAMPLE_COMMAND_ERR_EID, "Invalid ground command code: CC = 1000");
+    UT_CheckEvent_Setup(&EventTest, SAMPLE_COMMAND_ERR_EID, "Invalid ground command code: CC = %d");
     UT_SetDeferredRetcode(UT_KEY(CFE_SB_GetCmdCode), 1, 1000);
     SAMPLE_ProcessGroundCommand(&TestMsg.Base);
 
@@ -497,7 +506,7 @@ void Test_SAMPLE_VerifyCmdLength(void)
      */
     UT_SetDeferredRetcode(UT_KEY(CFE_SB_GetTotalMsgLength), 1, sizeof(TestMsg));
     UT_CheckEvent_Setup(&EventTest, SAMPLE_LEN_ERR_EID,
-                        "Invalid Msg length: ID = 0xFFFFFFFF,  CC = 0, Len = 18, Expected = 8");
+                        "Invalid Msg length: ID = 0x%X,  CC = %d, Len = %d, Expected = %d");
 
     SAMPLE_VerifyCmdLength(&TestMsg, sizeof(TestMsg));