MSG missing branch coverage, would require alternate/stub implementation and splitting up coverage executable

[skliper]

Is your feature request related to a problem? Please describe.
The software is implemented to support multiple options but currently just utilizes a single option to build one executable (see issue #1886) which means it's impossible to cover all the branches.

Example - can't hit the non-success case of the following branch since the selected implementation for CFE_MSG_GetType used internally can't fail (although conceptually an implementation could test the header version and reject if it doesn't match for example):

cFE/modules/msg/fsw/src/cfe_msg_sechdr_checksum.c

Lines 79 to 83 in 5e41330

	status = CFE_MSG_GetType(MsgPtr, &type);
	if (status != CFE_SUCCESS || type != CFE_MSG_Type_Cmd || !hassechdr)
	{
	return CFE_MSG_WRONG_MSG_TYPE;
	}

Describe the solution you'd like
This could be solved by implementing #1886 (related to #631)

Describe alternatives you've considered
None

Additional context
Results in 6 branches not being exercised.

Requester Info
Jacob Hageman - NASA/GSFC

[avan989]

The current call to CFE_MSG_GetType in CFE_MSG_GenerateChecksum is to cfe/modules/msg/fsw/src/cfe_msg_ccsdspri.c. This function only returns CFE_SUCCESS. Cannot hit the Non-success case for "status" in CFE_MSG_GenerateChecksum with the current build. Full code coverage is not possible unless we follow what @skliper recommends or rewrite CFE_MSG_GenerateCheckSum. @dmknutsen @dzbaker

cFE/modules/msg/fsw/src/cfe_msg_ccsdspri.c

Lines 117 to 135 in 5e41330

	CFE_Status_t CFE_MSG_GetType(const CFE_MSG_Message_t *MsgPtr, CFE_MSG_Type_t *Type)
	{
	if (MsgPtr == NULL || Type == NULL)
	{
	return CFE_MSG_BAD_ARGUMENT;
	}
	if ((MsgPtr->CCSDS.Pri.StreamId[0] & (CFE_MSG_TYPE_MASK >> 8)) != 0)
	{
	*Type = CFE_MSG_Type_Cmd;
	}
	else
	{
	*Type = CFE_MSG_Type_Tlm;
	}
	return CFE_SUCCESS;
	}