suite: fix deadlock in suite.Require()/Assert()

As pointed out in issue #1520, if the suite is not initialised properly
(buy calling the Run function), then calling suite.Require() or
suite.Assert() will result in a deadlock.

This commit fixes that by panicking if the suite is not initialised
properly. This is justified because, the suite is intended to be
triggered in the right way. If the user does not do that, this panic will
nudge them in the right direction.

It has to be a panic because, at this point, we don't have access to any
testing.T context to gracefully call a t.Fail(). Also, these two
functions are not expected to return an error.

Fixes #1520

suite/suite.go

@@ -58,7 +58,7 @@ func (suite *Suite) Require() *require.Assertions {
 	suite.mu.Lock()
 	defer suite.mu.Unlock()
 	if suite.require == nil {
-		suite.require = require.New(suite.T())
+		panic("'Require' must not be called before 'Run' or 'SetT'")
 	}
 	return suite.require
 }
@@ -72,7 +72,7 @@ func (suite *Suite) Assert() *assert.Assertions {
 	suite.mu.Lock()
 	defer suite.mu.Unlock()
 	if suite.Assertions == nil {
-		suite.Assertions = assert.New(suite.T())
+		panic("'Assert' must not be called before 'Run' or 'SetT'")
 	}
 	return suite.Assertions
 }

suite/suite_test.go

@@ -692,3 +692,27 @@ func TestSubtestPanic(t *testing.T) {
 	assert.True(t, suite.inTearDownTest)
 	assert.True(t, suite.inTearDownSuite)
 }
+
+type unInitialisedSuite struct {
+	Suite
+}
+
+// TestUnInitialisedSuites asserts the behaviour of the suite methods when the
+// suite is not initialised
+func TestUnInitialisedSuites(t *testing.T) {
+	t.Run("should panic on Require", func(t *testing.T) {
+		suite := new(unInitialisedSuite)
+
+		assert.Panics(t, func() {
+			suite.Require().True(true)
+		})
+	})
+
+	t.Run("should panic on Assert", func(t *testing.T) {
+		suite := new(unInitialisedSuite)
+
+		assert.Panics(t, func() {
+			suite.Assert().True(true)
+		})
+	})
+}