[test] Enable EMTEST_SKIP_CCACHE to skip ccache tests. NFC

We will likely use this on the emscripten-releases.

test/test_other.py

@@ -142,43 +142,39 @@ def metafunc(self, backend, *args, **kwargs):
   return metafunc
 
 
-def requires_ninja(func):
-  assert callable(func)
+def requires_tool(tool):
+  assert not callable(tool)
 
-  @wraps(func)
-  def decorated(self, *args, **kwargs):
-    if not shutil.which('ninja'):
-      self.fail('test requires ninja to be installed (available in PATH)')
-    return func(self, *args, **kwargs)
+  def decorate(func):
+    assert callable(func)
 
-  return decorated
+    @wraps(func)
+    def decorated(self, *args, **kwargs):
+      if not shutil.which(tool):
+        if f'EMTEST_SKIP_{tool.upper()}' in os.environ:
+          self.skipTest(f'test requires ccache and EMTEST_SKIP_{tool.upper()} is set')
+        else:
+          self.fail(f'{tool} required to run this test.  Use EMTEST_SKIP_{tool.upper()} to skip')
+      return func(self, *args, **kwargs)
 
+    return decorated
 
-def requires_ccache(func):
-  assert callable(func)
+  return decorate
 
-  @wraps(func)
-  def decorated(self, *args, **kwargs):
-    if not shutil.which('ccache'):
-      self.fail('test requires ccache to be installed (available in PATH)')
-    return func(self, *args, **kwargs)
 
-  return decorated
+def requires_ninja(func):
+  assert callable(func)
+  return requires_tool('ninja')(func)
 
 
-def requires_scons(func):
+def requires_ccache(func):
   assert callable(func)
+  return requires_tool('ccache')(func)
 
-  @wraps(func)
-  def decorated(self, *args, **kwargs):
-    if not shutil.which('scons'):
-      if 'EMTEST_SKIP_SCONS' in os.environ:
-        self.skipTest('test requires scons and EMTEST_SKIP_SCONS is set')
-      else:
-        self.fail('scons required to run this test.  Use EMTEST_SKIP_SCONS to skip')
-    return func(self, *args, **kwargs)
 
-  return decorated
+def requires_scons(func):
+  assert callable(func)
+  return requires_tool('scons')(func)
 
 
 def requires_pkg_config(func):