add two test:

zero denominator assert fail,
float type compile failure

tests/rational/trat_float.nim

@@ -0,0 +1,9 @@
+discard """
+  file: "trat_float.nim"
+  line: "9,19"
+  errormsg: '''type mismatch: got'''
+"""
+import rationals
+var
+  # this fails - no floats as num or den
+  r = initRational(1.0'f, 1.0'f)

tests/rational/trat_init.nim

@@ -0,0 +1,10 @@
+discard """
+  file: "trat_init.nim"
+  exitcode: "1"
+"""
+import rationals
+var
+  z = Rational[int](num: 0, den: 1)
+  o = initRational(num=1, den=1)
+  a = initRational(1, 2)
+  r = initRational(1, 0)  # this fails - no zero denominator