tests: Update test runner to fail early if prerequisites are missing

This change updates the test runner script to check for the presence of
required compilers (clang, gcc) before running tests.

Author: jcfr

run-tests.py

@@ -1,6 +1,7 @@
 
 import glob
 import os
+import shutil
 import subprocess
 import sys
 
@@ -13,6 +14,19 @@ def cleanup(out):
     ret = ret + s
   return ret
 
+
+# Check for required compilers and exit if any are missing
+CLANG_EXE = shutil.which('clang')
+if not CLANG_EXE:
+  sys.exit('Failed to run tests: clang compiler not found')
+
+GCC_EXE = shutil.which('gcc')
+if not GCC_EXE:
+  sys.exit('Failed to run tests: gcc compiler not found')
+
+SIMPLECPP_EXE = './simplecpp'
+
+
 commands = []
 
 for f in sorted(glob.glob(os.path.expanduser('testsuite/clang-preprocessor-tests/*.c*'))):
@@ -102,12 +116,12 @@ def run(compiler_executable, compiler_args):
     numberOfSkipped = numberOfSkipped + 1
     continue
 
-  clang_output = run('clang', cmd.split(' '))[1]
+  clang_output = run(CLANG_EXE, cmd.split(' '))[1]
 
-  gcc_output = run('gcc', cmd.split(' '))[1]
+  gcc_output = run(GCC_EXE, cmd.split(' '))[1]
 
   # -E is not supported and we bail out on unknown options
-  simplecpp_ec, simplecpp_output, simplecpp_err = run('./simplecpp', cmd.replace('-E ', '', 1).split(' '))
+  simplecpp_ec, simplecpp_output, simplecpp_err = run(SIMPLECPP_EXE, cmd.replace('-E ', '', 1).split(' '))
 
   if simplecpp_output != clang_output and simplecpp_output != gcc_output:
     filename = cmd[cmd.rfind('/')+1:]