Add Luacheck as a linting tool.

For #4

.pre-commit-config.yaml

@@ -0,0 +1,5 @@
+repos:
+- repo: https://github.com/lunarmodules/luacheck
+  rev: "v1.1.1"
+  hooks:
+  - id: luacheck

lua/luatest/reporter.lua

@@ -72,8 +72,8 @@ function Reporter._read_stderr(self) return self._stderr_stringio:value() end
 -- with the other diagnostic information when failures occur.
 function Reporter.capture_standard_files(self)
     if self:_should_capture() then
-        io.stdout = self._stdout_stringio
-        io.stderr = self._stderr_stringio
+        io.stdout = self._stdout_stringio -- luacheck: ignore 122
+        io.stderr = self._stderr_stringio -- luacheck: ignore 122
 
         -- print seems to operate separately from io.stdout|stderr.
         -- Replace the global print function with a function that writes

tests/test_collection.lua

@@ -81,8 +81,10 @@ function tests.test_module_does_not_have_test()
         tests = {["test_does_not_exist"] = true}
     }, test_modules, reporter)
 
-    assert.spy(reporter.error).was_called_with(reporter,
-                                               "tests/demo/something_test.lua has no test function named test_does_not_exist")
+    local expected =
+        "tests/demo/something_test.lua has no test function named test_does_not_exist"
+    assert.spy(reporter.error).was_called_with(reporter, expected)
+
 end
 
 -- A module that doesn't look like a table of functions triggers a warning.
@@ -129,7 +131,7 @@ function tests.test_reports_errors()
     spy.on(reporter, "error")
     spy.on(reporter, "fatal")
 
-    local test_count = collection.report_errors(errors, reporter)
+    collection.report_errors(errors, reporter)
 
     assert.spy(reporter.error).was_called_with(reporter,
                                                "Houston, we have a problem.")

tests/test_reporter.lua

@@ -74,7 +74,7 @@ function tests.test_fatal()
     assert.is_equal("\x1B[0m\x1B[31ma fatal error\x1B[0m\n", get_content(file))
     assert.stub(os.exit).was_called_with(1)
 
-    os.exit:revert()
+    os.exit:revert() -- luacheck: ignore 143
 end
 
 -- Start collection reports the tests directory.