Execute AM/PM Dates tests in the C locale. (#34371)

Author: maleadt

stdlib/Dates/test/io.jl

@@ -515,25 +515,36 @@ end
 end
 
 @testset "AM/PM" begin
-    for (t12,t24) in (("12:00am","00:00"), ("12:07am","00:07"), ("01:24AM","01:24"),
-                      ("12:00pm","12:00"), ("12:15pm","12:15"), ("11:59PM","23:59"))
-        d = DateTime("2018-01-01T$t24:00")
-        t = Time("$t24:00")
-        for HH in ("HH","II")
-            @test DateTime("2018-01-01 $t12","yyyy-mm-dd $HH:MMp") == d
-            @test Time("$t12","$HH:MMp") == t
+    # get the current locale
+    LC_TIME = 2
+    time_locale = ccall(:setlocale, Cstring, (Cint, Cstring), LC_TIME, C_NULL)
+    try
+        # set the locale
+        ccall(:setlocale, Cstring, (Cint, Cstring), LC_TIME, "C")
+
+        for (t12,t24) in (("12:00am","00:00"), ("12:07am","00:07"), ("01:24AM","01:24"),
+                        ("12:00pm","12:00"), ("12:15pm","12:15"), ("11:59PM","23:59"))
+            d = DateTime("2018-01-01T$t24:00")
+            t = Time("$t24:00")
+            for HH in ("HH","II")
+                @test DateTime("2018-01-01 $t12","yyyy-mm-dd $HH:MMp") == d
+                @test Time("$t12","$HH:MMp") == t
+            end
+            tmstruct = Libc.strptime("%I:%M%p", t12)
+            @test Time(tmstruct) == t
+            @test uppercase(t12) == Dates.format(t, "II:MMp") ==
+                                    Dates.format(d, "II:MMp") ==
+                Libc.strftime("%I:%M%p", tmstruct)
         end
-        tmstruct = Libc.strptime("%I:%M%p", t12)
-        @test Time(tmstruct) == t
-        @test uppercase(t12) == Dates.format(t, "II:MMp") ==
-                                Dates.format(d, "II:MMp") ==
-              Libc.strftime("%I:%M%p", tmstruct)
-    end
-    for bad in ("00:24am", "00:24pm", "13:24pm", "2pm", "12:24p.m.", "12:24 pm", "12:24pµ")
-        @eval @test_throws ArgumentError Time($bad, "II:MMp")
+        for bad in ("00:24am", "00:24pm", "13:24pm", "2pm", "12:24p.m.", "12:24 pm", "12:24pµ")
+            @eval @test_throws ArgumentError Time($bad, "II:MMp")
+        end
+        # if am/pm is missing, defaults to 24-hour clock
+        @eval Time("13:24", "II:MMp") == Time("13:24", "HH:MM")
+    finally
+        # recover the locale
+        ccall(:setlocale, Cstring, (Cint, Cstring), LC_TIME, time_locale)
     end
-    # if am/pm is missing, defaults to 24-hour clock
-    @eval Time("13:24", "II:MMp") == Time("13:24", "HH:MM")
 end
 
 end