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| >Hints On Writing A Test Case</H1 |
| ><P |
| >It is safest to write patterns that match all the output |
| generated by the tested program; this is called closure. |
| If a pattern does not match the entire output, any output that |
| remains will be examined by the next <B |
| CLASS="COMMAND" |
| >expect</B |
| > |
| command. In this situation, the precise boundary that determines |
| which <B |
| CLASS="COMMAND" |
| >expect</B |
| > command sees what is very |
| sensitive to timing between the Expect task and the task running |
| the tested tool. As a result, the test may sometimes appear to |
| work, but is likely to have unpredictable results. (This problem |
| is particularly likely for interactive tools, but can also |
| affect batch tools---especially for tests that take a long time |
| to finish.) The best way to ensure closure is to use the |
| <TT |
| CLASS="OPTION" |
| >-re</TT |
| > option for the <B |
| CLASS="COMMAND" |
| >expect</B |
| > |
| command to write the pattern as a full regular expressions; then |
| you can match the end of output using a <I |
| CLASS="EMPHASIS" |
| >$</I |
| >. |
| It is also a good idea to write patterns that match all |
| available output by using <I |
| CLASS="EMPHASIS" |
| >.*\</I |
| > after the |
| text of interest; this will also match any intervening blank |
| lines. Sometimes an alternative is to match end of line using |
| <I |
| CLASS="EMPHASIS" |
| >\r</I |
| > or <I |
| CLASS="EMPHASIS" |
| >\n</I |
| >, but this is |
| usually too dependent on terminal settings.</P |
| ><P |
| >Always escape punctuation, such as <I |
| CLASS="EMPHASIS" |
| >(</I |
| > |
| or <I |
| CLASS="EMPHASIS" |
| >"</I |
| >, in your patterns; for example, write |
| <I |
| CLASS="EMPHASIS" |
| >\(</I |
| >. If you forget to escape punctuation, |
| you will usually see an error message like <TABLE |
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| ><TR |
| ><TD |
| ><PRE |
| CLASS="PROGRAMLISTING" |
| >extra |
| characters after close-quote.</PRE |
| ></TD |
| ></TR |
| ></TABLE |
| ></P |
| ><P |
| >If you have trouble understanding why a pattern does not |
| match the program output, try using the <TT |
| CLASS="OPTION" |
| >--debug</TT |
| > |
| option to <B |
| CLASS="COMMAND" |
| >runtest</B |
| >, and examine the debug log |
| carefully.</P |
| ><P |
| >Be careful not to neglect output generated by setup rather |
| than by the interesting parts of a test case. For example, |
| while testing GDB, I issue a send <I |
| CLASS="EMPHASIS" |
| >set height |
| 0\n</I |
| > command. The purpose is simply to make sure GDB |
| never calls a paging program. The <I |
| CLASS="EMPHASIS" |
| >set |
| height</I |
| > command in GDB does not generate any |
| output; but running any command makes GDB issue a new |
| <I |
| CLASS="EMPHASIS" |
| >(gdb) </I |
| > prompt. If there were no |
| <B |
| CLASS="COMMAND" |
| >expect</B |
| > command to match this prompt, the |
| output <I |
| CLASS="EMPHASIS" |
| >(gdb) </I |
| > begins the text seen by the |
| next <B |
| CLASS="COMMAND" |
| >expect</B |
| > command---which might make that |
| pattern fail to match.</P |
| ><P |
| >To preserve basic sanity, I also recommended that no test |
| ever pass if there was any kind of problem in the test case. To |
| take an extreme case, tests that pass even when the tool will |
| not spawn are misleading. Ideally, a test in this sort of |
| situation should not fail either. Instead, print an error |
| message by calling one of the DejaGnu procedures |
| <B |
| CLASS="COMMAND" |
| >error</B |
| > or <B |
| CLASS="COMMAND" |
| >warning</B |
| >.</P |
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