diff --git a/runtime/vm_array_test.go b/runtime/vm_array_test.go
index d8ba8d0..2fe32e4 100644
--- a/runtime/vm_array_test.go
+++ b/runtime/vm_array_test.go
@@ -1,44 +1,42 @@
 package runtime_test
 
 import (
+	"fmt"
 	"testing"
 )
 
 func TestArray(t *testing.T) {
 	expect(t, `out = [1, 2 * 2, 3 + 3]`, ARR{1, 4, 6})
 
-	expect(t, `out = [1, 2, 3][0]`, 1)
-	expect(t, `out = [1, 2, 3][1]`, 2)
-	expect(t, `out = [1, 2, 3][2]`, 3)
-	expect(t, `i := 0; out = [1, 2, 3][i]`, 1)
-	expect(t, `out = [1, 2, 3][1 + 1]`, 3)
-	expect(t, `arr := [1, 2, 3]; out = arr[2]`, 3)
-	expect(t, `arr := [1, 2, 3]; out = arr[0] + arr[1] + arr[2]`, 6)
-	expect(t, `arr := [1, 2, 3]; i := arr[0]; out = arr[i]`, 2)
-
-	expect(t, `out = [1, 2, 3][1+1]`, 3)
-	expect(t, `a := 1; out = [1, 2, 3][a+1]`, 3)
-
-	expect(t, `out = [1, 2, 3][:]`, ARR{1, 2, 3})
-	expect(t, `out = [1, 2, 3][0:3]`, ARR{1, 2, 3})
-	expect(t, `out = [1, 2, 3][1:]`, ARR{2, 3})
-	expect(t, `out = [1, 2, 3][1:2]`, ARR{2})
-	expect(t, `out = [1, 2, 3][:2]`, ARR{1, 2})
-	expect(t, `out = [1, 2, 3][1:1]`, ARR{})
-
-	expect(t, `out = [1, 2, 3][3-2:1+1]`, ARR{2})
-	expect(t, `a := 1; out = [1, 2, 3][a-1:a+1]`, ARR{1, 2})
-
 	// array copy-by-reference
 	expect(t, `a1 := [1, 2, 3]; a2 := a1; a1[0] = 5; out = a2`, ARR{5, 2, 3})
 	expect(t, `func () { a1 := [1, 2, 3]; a2 := a1; a1[0] = 5; out = a2 }()`, ARR{5, 2, 3})
 
-	expectError(t, `[1, 2, 3][3]`)
-	expectError(t, `[1, 2, 3][-1]`)
+	// index operator
+	arr := ARR{1, 2, 3, 4, 5, 6}
+	arrStr := `[1, 2, 3, 4, 5, 6]`
+	arrLen := 6
+	for idx := 0; idx < arrLen; idx++ {
+		expect(t, fmt.Sprintf("out = %s[%d]", arrStr, idx), arr[idx])
+		expect(t, fmt.Sprintf("out = %s[0 + %d]", arrStr, idx), arr[idx])
+		expect(t, fmt.Sprintf("out = %s[1 + %d - 1]", arrStr, idx), arr[idx])
+		expect(t, fmt.Sprintf("idx := %d; out = %s[idx]", idx, arrStr), arr[idx])
+	}
+	expectError(t, fmt.Sprintf("%s[%d]", arrStr, -1))
+	expectError(t, fmt.Sprintf("%s[%d]", arrStr, arrLen))
 
-	expectError(t, `[1, 2, 3][-1:]`)
-	expectError(t, `[1, 2, 3][:4]`)
-	expectError(t, `[1, 2, 3][-1:3]`)
-	expectError(t, `[1, 2, 3][0:4]`)
-	expectError(t, `[1, 2, 3][2:1]`)
+	// slice operator
+	for low := 0; low < arrLen; low++ {
+		for high := low; high <= arrLen; high++ {
+			expect(t, fmt.Sprintf("out = %s[%d:%d]", arrStr, low, high), arr[low:high])
+			expect(t, fmt.Sprintf("out = %s[0 + %d : 0 + %d]", arrStr, low, high), arr[low:high])
+			expect(t, fmt.Sprintf("out = %s[1 + %d - 1 : 1 + %d - 1]", arrStr, low, high), arr[low:high])
+			expect(t, fmt.Sprintf("out = %s[:%d]", arrStr, high), arr[:high])
+			expect(t, fmt.Sprintf("out = %s[%d:]", arrStr, low), arr[low:])
+			expect(t, fmt.Sprintf("out = %s[:]", arrStr), arr[:])
+		}
+	}
+	expectError(t, fmt.Sprintf("%s[%d:]", arrStr, -1))
+	expectError(t, fmt.Sprintf("%s[:%d]", arrStr, arrLen+1))
+	expectError(t, fmt.Sprintf("%s[%d:%d]", arrStr, 2, 1))
 }
diff --git a/runtime/vm_string_test.go b/runtime/vm_string_test.go
index 11d6f44..d84cd11 100644
--- a/runtime/vm_string_test.go
+++ b/runtime/vm_string_test.go
@@ -1,6 +1,7 @@
 package runtime_test
 
 import (
+	"fmt"
 	"testing"
 )
 
@@ -13,20 +14,31 @@ func TestString(t *testing.T) {
 	expect(t, `out = "Hello" != "Hello"`, false)
 	expect(t, `out = "Hello" != "World"`, true)
 
-	expect(t, `out = "abcde"[0]`, 'a')
-	expect(t, `out = "abcde"[4]`, 'e')
-	expectError(t, `out = "abcde"[-1]`)
-	expectError(t, `out = "abcde"[5]`)
+	// index operator
+	str := "abcdef"
+	strStr := `"abcdef"`
+	strLen := 6
+	for idx := 0; idx < strLen; idx++ {
+		expect(t, fmt.Sprintf("out = %s[%d]", strStr, idx), str[idx])
+		expect(t, fmt.Sprintf("out = %s[0 + %d]", strStr, idx), str[idx])
+		expect(t, fmt.Sprintf("out = %s[1 + %d - 1]", strStr, idx), str[idx])
+		expect(t, fmt.Sprintf("idx := %d; out = %s[idx]", idx, strStr), str[idx])
+	}
+	expectError(t, fmt.Sprintf("%s[%d]", strStr, -1))
+	expectError(t, fmt.Sprintf("%s[%d]", strStr, strLen))
 
-	expect(t, `out = "abcde"[:]`, "abcde")
-	expect(t, `out = "abcde"[0:5]`, "abcde")
-	expect(t, `out = "abcde"[1:]`, "bcde")
-	expect(t, `out = "abcde"[:4]`, "abcd")
-	expect(t, `out = "abcde"[1:4]`, "bcd")
-	expect(t, `out = "abcde"[2:3]`, "c")
-	expect(t, `out = "abcde"[2:2]`, "")
-	expectError(t, `out = "abcde"[-1:]`)
-	expectError(t, `out = "abcde"[:6]`)
-	expectError(t, `out = "abcde"[-1:6]`)
-	expectError(t, `out = "abcde"[3:2]`)
+	// slice operator
+	for low := 0; low < strLen; low++ {
+		for high := low; high <= strLen; high++ {
+			expect(t, fmt.Sprintf("out = %s[%d:%d]", strStr, low, high), str[low:high])
+			expect(t, fmt.Sprintf("out = %s[0 + %d : 0 + %d]", strStr, low, high), str[low:high])
+			expect(t, fmt.Sprintf("out = %s[1 + %d - 1 : 1 + %d - 1]", strStr, low, high), str[low:high])
+			expect(t, fmt.Sprintf("out = %s[:%d]", strStr, high), str[:high])
+			expect(t, fmt.Sprintf("out = %s[%d:]", strStr, low), str[low:])
+			expect(t, fmt.Sprintf("out = %s[:]", strStr), str[:])
+		}
+	}
+	expectError(t, fmt.Sprintf("%s[%d:]", strStr, -1))
+	expectError(t, fmt.Sprintf("%s[:%d]", strStr, strLen+1))
+	expectError(t, fmt.Sprintf("%s[%d:%d]", strStr, 2, 1))
 }