Test internal/datafiles, internal/datatype, internal/proven and internal/builtinfunc, and allow the root to import them

internal/datatype/datatype_test.go

@@ -0,0 +1,25 @@
+package datatype
+
+import "testing"
+
+func TestEachDatatypeIsSpelledAsDataWritesIt(t *testing.T) {
+	for d, want := range map[DataType][2]string{
+		String:  {"string", "text"},
+		Integer: {"integer", "an integer"},
+		Number:  {"number", "a number"},
+		Boolean: {"boolean", "a boolean"},
+	} {
+		if d.String() != want[0] || Noun(d) != want[1] {
+			t.Errorf("%d: String = %q, Noun = %q, want %q", int(d), d.String(), Noun(d), want)
+		}
+	}
+	if Count != 4 {
+		t.Errorf("Count = %d, want the four datatypes", Count)
+	}
+}
+
+func TestStringNamesADatatypeNoDataWrites(t *testing.T) {
+	if got := DataType(9).String(); got != "DataType(9)" {
+		t.Errorf("String = %q, want DataType(9)", got)
+	}
+}