fate: allow temp files for passed test to be kept

Set make variable KEEP to non-zero value to preserve temp files
when a test has passed.

Helpful in diagnosing failed tests when test outfile is some type of
single hash and does not reveal differences in processed output.

doc/fate.texi

@@ -222,6 +222,11 @@ Set to @samp{1} to generate the missing or mismatched references.
 Specify which hardware acceleration to use while running regression tests,
 by default @samp{none} is used.
 
+@item KEEP
+Set to @samp{1} to keep temp files generated by fate test(s) when test is successful.
+Default is @samp{0}, which removes these files. Files are always kept when a test
+fails.
+
 @end table
 
 @section Examples

tests/Makefile

@@ -225,7 +225,7 @@ FATE += $(FATE_HW-yes)
 $(FATE) $(FATE_TESTS-no): export PROGSUF = $(PROGSSUF)
 $(FATE) $(FATE_TESTS-no): $(FATE_UTILS:%=tests/%$(HOSTEXESUF))
 	@echo "TEST    $(@:fate-%=%)"
-	$(Q)$(SRC_PATH)/tests/fate-run.sh $@ "$(TARGET_SAMPLES)" "$(TARGET_EXEC)" "$(TARGET_PATH)" '$(CMD)' '$(CMP)' '$(REF)' '$(FUZZ)' '$(THREADS)' '$(THREAD_TYPE)' '$(CPUFLAGS)' '$(CMP_SHIFT)' '$(CMP_TARGET)' '$(SIZE_TOLERANCE)' '$(CMP_UNIT)' '$(GEN)' '$(HWACCEL)' '$(REPORT)'
+	$(Q)$(SRC_PATH)/tests/fate-run.sh $@ "$(TARGET_SAMPLES)" "$(TARGET_EXEC)" "$(TARGET_PATH)" '$(CMD)' '$(CMP)' '$(REF)' '$(FUZZ)' '$(THREADS)' '$(THREAD_TYPE)' '$(CPUFLAGS)' '$(CMP_SHIFT)' '$(CMP_TARGET)' '$(SIZE_TOLERANCE)' '$(CMP_UNIT)' '$(GEN)' '$(HWACCEL)' '$(REPORT)' '$(KEEP)'
 
 fate-list:
 	@printf '%s\n' $(sort $(FATE))

tests/fate-run.sh

@@ -25,6 +25,7 @@ cmp_unit=${15:-2}
 gen=${16:-no}
 hwaccel=${17:-none}
 report_type=${18:-standard}
+keep=${19:-0}
 
 outdir="tests/data/fate"
 outfile="${outdir}/${test}"
@@ -428,7 +429,9 @@ if test $err != 0 && test $gen != "no" ; then
 fi
 
 if test $err = 0; then
-    rm -f $outfile $errfile $cmpfile $cleanfiles
+    if test $keep = 0; then
+        rm -f $outfile $errfile $cmpfile $cleanfiles
+    fi
 elif test $gen = "no"; then
     echo "Test $test failed. Look at $errfile for details."
     test "${V:-0}" -gt 0 && cat $errfile