test: validate expected error message

make sure the error in tbs config tests is expected

Author: kruskall

internal/beater/config/sampling_test.go

@@ -39,7 +39,7 @@ func TestSamplingPoliciesValidation(t *testing.T) {
 		c, err := NewConfig(config.MustNewConfigFrom(map[string]interface{}{
 			"sampling.tail.enabled": true,
 		}), nil, logptest.NewTestingLogger(t, ""))
-		assert.Error(t, err)
+		assert.EqualError(t, err, "error processing configuration: invalid sampling.tail config: no policies specified accessing 'sampling.tail'")
 		assert.Nil(t, c)
 	})
 	t.Run("NoDefaultPolicies", func(t *testing.T) {
@@ -49,7 +49,7 @@ func TestSamplingPoliciesValidation(t *testing.T) {
 				"sample_rate":  0.5,
 			}},
 		}), nil, logptest.NewTestingLogger(t, ""))
-		assert.Error(t, err)
+		assert.EqualError(t, err, "error processing configuration: invalid sampling.tail config: no default (empty criteria) policy specified accessing 'sampling.tail'")
 		assert.Nil(t, c)
 	})
 }