promqltest: improve error messages when unexpected type is returned, and fix inverted expected and actual values in error message when scalar value does not match expected

Signed-off-by: Charles Korn <charles.korn@grafana.com>

promql/promqltest/test.go

@@ -650,8 +650,9 @@ type evalCmd struct {
 	expectedFailMessage string
 	expectedFailRegexp  *regexp.Regexp
 
-	metrics  map[uint64]labels.Labels
-	expected map[uint64]entry
+	metrics      map[uint64]labels.Labels
+	expectScalar bool
+	expected     map[uint64]entry
 }
 
 type entry struct {
@@ -695,12 +696,15 @@ func (ev *evalCmd) String() string {
 // expect adds a sequence of values to the set of expected
 // results for the query.
 func (ev *evalCmd) expect(pos int, vals ...parser.SequenceValue) {
+	ev.expectScalar = true
 	ev.expected[0] = entry{pos: pos, vals: vals}
 }
 
 // expectMetric adds a new metric with a sequence of values to the set of expected
 // results for the query.
 func (ev *evalCmd) expectMetric(pos int, m labels.Labels, vals ...parser.SequenceValue) {
+	ev.expectScalar = false
+
 	h := m.Hash()
 	ev.metrics[h] = m
 	ev.expected[h] = entry{pos: pos, vals: vals}
@@ -714,6 +718,10 @@ func (ev *evalCmd) compareResult(result parser.Value) error {
 			return fmt.Errorf("expected ordered result, but query returned a matrix")
 		}
 
+		if ev.expectScalar {
+			return fmt.Errorf("expected scalar result, but got matrix %s", val.String())
+		}
+
 		if err := assertMatrixSorted(val); err != nil {
 			return err
 		}
@@ -782,6 +790,10 @@ func (ev *evalCmd) compareResult(result parser.Value) error {
 		}
 
 	case promql.Vector:
+		if ev.expectScalar {
+			return fmt.Errorf("expected scalar result, but got vector %s", val.String())
+		}
+
 		seen := map[uint64]bool{}
 		for pos, v := range val {
 			fp := v.Metric.Hash()
@@ -820,15 +832,15 @@ func (ev *evalCmd) compareResult(result parser.Value) error {
 		}
 
 	case promql.Scalar:
-		if len(ev.expected) != 1 {
-			return fmt.Errorf("expected vector result, but got scalar %s", val.String())
+		if !ev.expectScalar {
+			return fmt.Errorf("expected vector or matrix result, but got %s", val.String())
 		}
 		exp0 := ev.expected[0].vals[0]
 		if exp0.Histogram != nil {
-			return fmt.Errorf("expected Histogram %v but got scalar %s", exp0.Histogram.TestExpression(), val.String())
+			return fmt.Errorf("expected histogram %v but got %s", exp0.Histogram.TestExpression(), val.String())
 		}
 		if !almost.Equal(exp0.Value, val.V, defaultEpsilon) {
-			return fmt.Errorf("expected Scalar %v but got %v", val.V, exp0.Value)
+			return fmt.Errorf("expected scalar %v but got %v", exp0.Value, val.V)
 		}
 
 	default:

promql/promqltest/test_test.go

@@ -554,6 +554,43 @@ eval range from 0 to 5m step 5m testmetric
 `,
 			expectedError: `error in eval testmetric (line 5): expected float value at index 0 for {__name__="testmetric"} to have timestamp 300000, but it had timestamp 0 (result has 1 float point [3 @[0]] and 1 histogram point [{count:0, sum:0} @[300000]])`,
 		},
+		"instant query with expected scalar result": {
+			input: `
+				eval instant at 1m 3
+					3
+			`,
+		},
+		"instant query with unexpected scalar result": {
+			input: `
+				eval instant at 1m 3
+					2
+			`,
+			expectedError: `error in eval 3 (line 2): expected scalar 2 but got 3`,
+		},
+		"instant query that returns a scalar but expects a vector": {
+			input: `
+				eval instant at 1m 3
+					{} 3
+			`,
+			expectedError: `error in eval 3 (line 2): expected vector or matrix result, but got scalar: 3 @[60000]`,
+		},
+		"instant query that returns a vector but expects a scalar": {
+			input: `
+				eval instant at 1m vector(3)
+					3
+			`,
+			expectedError: `error in eval vector(3) (line 2): expected scalar result, but got vector {} => 3 @[60000]`,
+		},
+		"range query that returns a matrix but expects a scalar": {
+			input: `
+				eval range from 0 to 1m step 30s vector(3)
+					3
+			`,
+			expectedError: `error in eval vector(3) (line 2): expected scalar result, but got matrix {} =>
+3 @[0]
+3 @[30000]
+3 @[60000]`,
+		},
 	}
 
 	for name, testCase := range testCases {