reftable/block_test.c exercises the functions defined in
reftable/block.{c, h}. Migrate reftable/block_test.c to the unit
testing framework. Migration involves refactoring the tests
to use the unit testing framework instead of reftable's test
framework and renaming the tests to follow the unit-tests'
naming conventions.

Mentored-by: Patrick Steinhardt <[email protected]>
Mentored-by: Christian Couder <[email protected]>
Signed-off-by: Chandra Pratap <[email protected]>

Harmonize the newly ported test unit-tests/t-reftable-block.c
with the following guidelines:
- Single line 'for' statements must omit curly braces.
- Structs must be 0-initialized with '= { 0 }' instead of '= { NULL }'.
- Array sizes and indices should preferably be of type 'size_t'and
  not 'int'.
- Return code variable should preferably be named 'ret', not 'n'.

Mentored-by: Patrick Steinhardt <[email protected]>
Mentored-by: Christian Couder <[email protected]>
Signed-off-by: Chandra Pratap <[email protected]>

Used block readers must be released using block_reader_release() to
prevent the occurence of a memory leak. Make test_block_read_write()
conform to this statement.

Mentored-by: Patrick Steinhardt <[email protected]>
Mentored-by: Christian Couder <[email protected]>
Signed-off-by: Chandra Pratap <[email protected]>

In the current testing setup, operations like read and write for
reftable blocks as defined by reftable/block.{c, h} are verified by
comparing only the keys of input and output reftable records. This is
not ideal because there can exist inequal reftable records with the
same key. Use the dedicated function for record comparison,
reftable_record_equal(), instead of key-based comparison.

Mentored-by: Patrick Steinhardt <[email protected]>
Mentored-by: Christian Couder <[email protected]>
Signed-off-by: Chandra Pratap <[email protected]>

In the current testing setup, the record key required for many block
iterator functions is manually stored in a strbuf struct and then
passed to these functions. This is not ideal when there exists a
dedicated function to encode a record's key into a strbuf, namely
reftable_record_key(). Use this function instead of manual encoding.

Mentored-by: Patrick Steinhardt <[email protected]>
Mentored-by: Christian Couder <[email protected]>
Signed-off-by: Chandra Pratap <[email protected]>

block_iter_reset() restores a block iterator to its state at the time
of initialization without freeing any memory while block_iter_close()
deallocates the memory for the iterator.

In the current testing setup, a block iterator is allocated and
deallocated for every iteration of a loop, which hurts performance.
Improve upon this by using block_iter_reset() at the start of each
iteration instead. This has the added benifit of testing
block_iter_reset(), which currently remains untested.

Similarly, remove reftable_record_release() for a reftable record
that is still in use.

Mentored-by: Patrick Steinhardt <[email protected]>
Mentored-by: Christian Couder <[email protected]>
Signed-off-by: Chandra Pratap <[email protected]>

Use xstrfmt() to assign a formatted string to a ref record's
refname instead of xstrdup(). This helps save the overhead of
a local 'char' buffer as well as makes the test more compact.

Mentored-by: Patrick Steinhardt <[email protected]>
Mentored-by: Christian Couder <[email protected]>
Signed-off-by: Chandra Pratap <[email protected]>

Currently, there are two variables for array indices, 'i' and 'j'.
The variable 'j' is used only once and can be easily replaced with
'i'. Get rid of 'j' and replace its occurence with 'i'.

Mentored-by: Patrick Steinhardt <[email protected]>
Mentored-by: Christian Couder <[email protected]>
Signed-off-by: Chandra Pratap <[email protected]>

In the current testing setup, block operations are only exercised
for ref blocks. Add another test that exercises these operations
for log blocks as well.

Mentored-by: Patrick Steinhardt <[email protected]>
Mentored-by: Christian Couder <[email protected]>
Signed-off-by: Chandra Pratap <[email protected]>

In the current testing setup, block operations are left unexercised
for obj blocks. Add a test that exercises these operations for obj
blocks.

Mentored-by: Patrick Steinhardt <[email protected]>
Mentored-by: Christian Couder <[email protected]>
Signed-off-by: Chandra Pratap <[email protected]>

In the current testing setup, block operations are left unexercised
for index blocks. Add a test that exercises these operations for
index blocks.

Mentored-by: Patrick Steinhardt <[email protected]>
Mentored-by: Christian Couder <[email protected]>
Signed-off-by: Chandra Pratap <[email protected]>