[R-package] silence logs in print(), show(), summary() tests (#5237)

R-package/tests/testthat/test_lgb.Booster.R

@@ -1255,24 +1255,64 @@ test_that("Booster's print, show, and summary work correctly", {
        )
     }
 
+    .has_expected_content_for_fitted_model <- function(printed_txt) {
+      expect_true(any(grepl("^LightGBM Model", printed_txt)))
+      expect_true(any(grepl("^Fitted to dataset", printed_txt)))
+    }
+
+    .has_expected_content_for_finalized_model <- function(printed_txt) {
+      expect_true(any(grepl("^LightGBM Model$", printed_txt)))
+      expect_true(any(grepl("Booster handle is invalid", printed_txt)))
+    }
+
     .check_methods_work <- function(model) {
 
-        # should work for fitted models
+        #--- should work for fitted models --- #
+
+        # print()
+        log_txt <- capture.output({
           ret <- print(model)
+        })
         .have_same_handle(ret, model)
+        .has_expected_content_for_fitted_model(log_txt)
+
+        # show()
+        log_txt <- capture.output({
           ret <- show(model)
+        })
         expect_null(ret)
+        .has_expected_content_for_fitted_model(log_txt)
+
+        # summary()
+        log_text <- capture.output({
           ret <- summary(model)
+        })
         .have_same_handle(ret, model)
+        .has_expected_content_for_fitted_model(log_txt)
 
-        # should not fail for finalized models
+        #--- should not fail for finalized models ---#
         model$finalize()
+
+        # print()
+        log_txt <- capture.output({
           ret <- print(model)
+        })
+        .has_expected_content_for_finalized_model(log_txt)
+
+        # show()
         .have_same_handle(ret, model)
+        log_txt <- capture.output({
           ret <- show(model)
+        })
         expect_null(ret)
+        .has_expected_content_for_finalized_model(log_txt)
+
+        # summary()
+        log_txt <- capture.output({
           ret <- summary(model)
+        })
         .have_same_handle(ret, model)
+        .has_expected_content_for_finalized_model(log_txt)
     }
 
     data("mtcars")