Removing usage of yield in test_utils.py

[kaushik94]

Please take a look at #233. Also added a test for species_tuple_to_string. @wkerzendorf please take a look.

[kaushik94]

Works perfect now( with the fix also in #232 )

kaushik@ghost:~/Desktop/soc/tardis/tardis/tests$ py.test -q test_util.py
..................
18 passed in 0.69 seconds

@wkerzendorf please take a look.

[landscape-bot]

Repository health decreased by 0.01% when pulling d20a187 on kaushik94:tuple_to_string into 1cfef3b on tardis-sn:master.

• 233 new problems were found (including 17 errors and 97 code smells).
• 233 problems were fixed (including 17 errors and 97 code smells).

[kaushik94]

@wkerzendorf The test_utils.py doesn't work currently even if we plug in the wrong values, because of the usage of yield and I think this PR solves it. I think we should merge it before we make any major changes to the files. What do you think ?

[coveralls]

Changes Unknown when pulling d20a187 on kaushik94:tuple_to_string into * on tardis-sn:master*.

[wkerzendorf]

@kaushik94 well done!

[kaushik94]

Thanks @wkerzendorf .