Refactor tests

Organize tests into subdirectories and use a new makefile that scans
.sby files and allows selecting tests by mode, engine, solver and/or
subdirectory. Automatically skips tests that use engines/solvers that
are not found in the PATH.

See `cd tests; make help` for a description of supported make targets.

tests/keepgoing/keepgoing_multi_step.py

@@ -0,0 +1,31 @@
+import sys
+from check_output import *
+
+src = "keepgoing_multi_step.sv"
+
+workdir = sys.argv[1]
+
+assert_0 = line_ref(workdir, src, "assert(0)")
+step_3_7 = line_ref(workdir, src, "step 3,7")
+step_5 = line_ref(workdir, src, "step 5")
+step_7 = line_ref(workdir, src, "step 7")
+
+log = open(workdir + "/logfile.txt").read()
+log_per_trace = log.split("Writing trace to VCD file")[:-1]
+
+assert len(log_per_trace) == 4
+
+
+assert re.search(r"Assert failed in test: %s \(.*\)$" % assert_0, log_per_trace[0], re.M)
+
+for i in range(1, 4):
+    assert re.search(r"Assert failed in test: %s \(.*\) \[failed before\]$" % assert_0, log_per_trace[i], re.M)
+
+
+assert re.search(r"Assert failed in test: %s \(.*\)$" % step_3_7, log_per_trace[1], re.M)
+assert re.search(r"Assert failed in test: %s \(.*\)$" % step_5, log_per_trace[2], re.M)
+assert re.search(r"Assert failed in test: %s \(.*\) \[failed before\]$" % step_3_7, log_per_trace[3], re.M)
+assert re.search(r"Assert failed in test: %s \(.*\)$" % step_7, log_per_trace[3], re.M)
+
+pattern = f"Property ASSERT in test at {assert_0} failed. Trace file: engine_0/trace0.vcd"
+assert re.search(pattern, open(f"{workdir}/{workdir}.xml").read())