33.3. Variant Comparison Files

33.3. Variant Comparison Files
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33.3. Variant Comparison Files #

+ Since some of the tests inherently produce environment-dependent + results, we have provided ways to specify alternate “expected” + result files. Each regression test can have several comparison files + showing possible results on different platforms. There are two + independent mechanisms for determining which comparison file is used + for each test. +

+ The first mechanism allows comparison files to be selected for + specific platforms. There is a mapping file, + src/test/regress/resultmap, that defines + which comparison file to use for each platform. + To eliminate bogus test “failures” for a particular platform, + you first choose or make a variant result file, and then add a line to the + resultmap file. +

+ Each line in the mapping file is of the form +

+testname:output:platformpattern=comparisonfilename
+

+ The test name is just the name of the particular regression test + module. The output value indicates which output file to check. For the + standard regression tests, this is always out. The + value corresponds to the file extension of the output file. + The platform pattern is a pattern in the style of the Unix + tool expr (that is, a regular expression with an implicit + ^ anchor at the start). It is matched against the + platform name as printed by config.guess. + The comparison file name is the base name of the substitute result + comparison file. +

+ For example: some systems lack a working strtof function, + for which our workaround causes rounding errors in the + float4 regression test. + Therefore, we provide a variant comparison file, + float4-misrounded-input.out, which includes + the results to be expected on these systems. To silence the bogus + “failure” message on Cygwin + platforms, resultmap includes: +

+float4:out:.*-.*-cygwin.*=float4-misrounded-input.out
+

+ which will trigger on any machine where the output of + config.guess matches .*-.*-cygwin.*. + Other lines in resultmap select the variant comparison + file for other platforms where it's appropriate. +

+ The second selection mechanism for variant comparison files is + much more automatic: it simply uses the “best match” among + several supplied comparison files. The regression test driver + script considers both the standard comparison file for a test, + testname.out, and variant files named + testname_digit.out + (where the digit is any single digit + 0-9). If any such file is an exact match, + the test is considered to pass; otherwise, the one that generates + the shortest diff is used to create the failure report. (If + resultmap includes an entry for the particular + test, then the base testname is the substitute + name given in resultmap.) +

+ For example, for the char test, the comparison file + char.out contains results that are expected + in the C and POSIX locales, while + the file char_1.out contains results sorted as + they appear in many other locales. +

+ The best-match mechanism was devised to cope with locale-dependent + results, but it can be used in any situation where the test results + cannot be predicted easily from the platform name alone. A limitation of + this mechanism is that the test driver cannot tell which variant is + actually “correct” for the current environment; it will just pick + the variant that seems to work best. Therefore it is safest to use this + mechanism only for variant results that you are willing to consider + equally valid in all contexts. +

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